The episode starts at Tegridy Farms where Randy has a meeting with the family. He explains, since they're no longer selling to China, they are not selling enough weed to make up their costs, and asks the family for ideas. After deciding Stan and Sharon's ideas aren't good enough, he asks Towelie, who suggests using the parts of the weed that goes to waste. Randy accepts the idea.
At school, Cartman and Butters are celebrating Sloppy Joes day, only to receive fish when they reach the cafeteria, due to students complaining about the food options. Cartman realises the girls where the ones who protested and confront them. As he is yelling at them, he gets a heart attack, but is resuscitated soon after.
Randy and Towelie discuss in the car about how much money they can get from the mulch. Randy finds himself hungry and decides to stop off at Burger King. There, he decides to try the Impossiburger, a plant-based burger. He finds it tastes like shit, and, when realising how much the burger makes, he comes up with an idea.
Cartman returns to school from the hospital. Nichole overhears him saying the girls tried to kill him, and yell at him, explaining its not only girls that protest. A Vegan Boy backs her up, which sparks an argument. Mr. Mackey comes to break it up, explaining the school lunches will not be changed. This angers the girls, but Mr. Mackey explains that his main focus is the health of his students.
Randy invites Gerald to the farm so he can show off the new plant-based burger he's made using the mulch. At first, Gerald finds it tastes like shit, but after a few bites, the burger gets him high, making him enjoy the burger a lot more. Randy then opens a stall outside the Burger King which gets a lot of customers, much to the annoyance of Rick.
At school, Cartman is enjoying barbeque ribs. Wendy then gives a speech about their generation and how they should be eating better. This angers Cartman to the point where he has a second heart attack, but is resuscitated again.
To try and make peace regarding the school dinners protests, PC Principal brings in the Goo Man, who explains about his goo and how the food it makes tastes exactly the same as normal food. The school worry that Cartman will not be happy about the new dinners, so they decide not to tell him.
When Cartman returns from the hospital, he gets excited about Taco Tuesday. He notices the tacos taste different, but the cafeteria worker explains its Incredible Meat. Cartman then starts eating the tacos, with the whole school watching him, worried he will notice the difference. He doesn't.
After Randy persuades the town to adapt a vegan diet, he opens his own burger shop opposite Burger King. The business receives a large amount of customers, which in turn leads to other food places being empty. The Goo Man tries to make a deal with City Wok, only to find it has no customers due to Tegridy Burger.
The rancher visits Tegridy Farms to yell at Randy about putting him out of business with his plant-based burgers. He explains he has loads of cows that he no longer needs, so he dumps them on the farm for Randy to deal with. Randy and Towelie decide to get high and kill all the cows.
Cartman notices Butters isn't as excited about the school meals as he used to be, leading Butters to tell the truth about the food he's been eating. The Goo Man speaks to Cartman at Burger King, explaining that his goo is actually full of fat, and that he's been selling the food all over town. The rancher then turns up, explaining to the Goo man that he has done what he needed to do. The Goo Man leaves to finish his plan, while Cartman goes to speak to the school.
Tegridy Burger has become the most popular burger in Colorado, and a reporter comes to interview Randy. Rick turns up to show everyone the tape of Randy and Towelie killing the cows, leading people to assume Tegridy Burgers were made of meat. The public then boo Randy.
Cartman arrives at the cafeteria and tells them he knows what's in the food. Mr. Mackey tries to apologize, but Cartman explains he is the one who is apologising. He tells the kids that he doesn't care, since all he wanted is the same food as he was eating before, fatty, rubbish food that comes in a box, and the new food is still fatty and rubbish. This disappoints the kids, who thought they were being healthier.
AV Club gave "Let Them Eat Goo" a "B+" rating saying: "While not quite as funny as last week’s episode, “Let Them Eat Goo” continues Season 23's winning streak. Cartman’s violent reactions to healthier food show him at his terror-inducing best, while the resolution to his plot is clever and unexpected. Randy’s escapades continue to be quite enjoyable as well."