Cook the pasta according to the package directions in salted water, leaving a little firmer than usual. This will ensure the pasta does not overcook in the crockpot later. Drain and set aside.
In a large skillet, heat the oil until hot and it begins to shimmer. Add the ground beef, season with the salt and pepper. Cook until the beef has browned, about 8 minutes. Using a slotted spoon, remove the beef to a paper towel-lined plate.
In the same pan, cook the onions and garlic over medium high heat until translucent and cooked through, about 10 minutes.
Add the pizza sauce, cooked beef, and Italian seasoning, bring to a simmer, then remove from the heat.
Spray the inside of the crockpot, then add the cooked pasta, beef sauce, and ½ cup of the cheese. Stir together.
Sprinkle the rest of the cheese over the top, then arrange the pepperoni over the cheese.
Cover and cook on low for about 3 hours, or high for 1 ½ to 2 hours. It should be heated throughout and the cheese completely melted.
Top with the basil and serve.