Bring a large pot of lightly salted water to a boil. Cook pasta shells in the boiling water, stirring occasionally until cooked through but firm to the bite, about 8 minutes. Drain.
Cook and stir ground beef, bell pepper, onion, and salt in a skillet over medium heat until beef is browned and crumbly, 5 to 10 minutes; drain. Mix kidney beans, mozzarella cheese, and pesto into ground beef mixture.
Spoon 1/4 cup ground beef mixture into each pasta shell. Arrange stuffed shells in a serving dish and top with pasta sauce and Parmesan cheese.