Preheat the broiler and position a rack about 6 inches from the heat source.
Prepare 16 ounces of pasta according to package directions; drain and set aside.
Place the jar of Prego pasta sauce in a saucepan and heat over medium until warmed through, stirring occasionally.
Divide the cooked pasta among four oven-proof bowls or ramekins.
Spoon warmed pasta sauce over each bowl of pasta, then evenly distribute the chopped onion, chopped bell pepper, sliced mushrooms, cooked Italian sausage, and pepperoni on top.
Top each bowl with the shredded or sliced mozzarella cheese.
Place the bowls on a baking sheet and broil for about 5 to 7 minutes, watching closely, until the cheese is melted and beginning to brown.
Carefully remove from the oven and let cool briefly before serving.