Preheat the oven to 350 degrees F and lightly grease a 9x13 baking dish with cooking spray.
Bring a large pot of salted water to a boil. Add the pasta shells and cook until tender, about 10 to 12 minutes, stirring occasionally. Drain and transfer shells to the prepared baking dish, then stir in the butter until melted.
Next, add the ground beef, diced red onion, and minced garlic to a frying pan and cook over medium-high heat until beef is browned, about 7 to 10 minutes. Break the beef up into small chunks as it cooks.
In the meantime, add cubed Velveeta and milk to a medium saucepan and cook over medium heat until cheese is melted, stirring occasionally, about 8 to 10 minutes. Then turn heat to low and stir in ketchup, Worcestershire sauce, paprika, salt, and cooked ground beef with onions and garlic.
Pour the cheese sauce over the pasta shells in the baking dish. Stir to combine until the shells are thoroughly coated in cheese sauce. Then bake in the oven for 10 minutes to help the sauce soak into the pasta.
Serve hot or store in the fridge for up to 5 days.
Notes
Reheating: You can easily reheat single servings of this cheeseburger mac and cheese by microwaving for 1 to 2 minutes, stirring halfway through.