Step 1

Preheat oven to 350 degrees. Spray a baking sheet with nonstick spray.

Step 2

Bring a skillet sprayed with nonstick spray to medium heat. Add onion, bell pepper, and mushrooms. Cook and stir until softened and lightly browned, about 4 minutes.

Step 3

Transfer cooked veggies to a large bowl. Add beef, chopped pepperoni, egg substitute, garlic powder, basil, and salt. Mix thoroughly. Firmly and evenly form into 24 meatballs, and place them evenly spaced on the baking sheet.

Step 4

Bake for 10 minutes.

Step 5

Gently flip meatballs, and arrange them closely in the center of the sheet. Evenly top with sauce and cheese. Bake until meatballs are cooked through, sauce is hot, and cheese has melted, about 5 minutes.