Cook the pasta al dente according to the instructions on the package.
Preheat to oven to 375 ˚F. Oil a 9 x13 oven baking dish.
In a skillet over medium-high heat, add the olive oil. Once hot, add the beef and the onion, and cook until the beef is completely cooked, about 10 minutes. Set aside.
In a medium bowl, add the tomato, oregano, garlic powder, onion powder, salt and pepper. Stir to combine all the ingredients.
In a large bowl, add the cooked pasta, tomato sauce, and chopped green pepper. Stir until the pasta is coated with the sauce.
Add the pasta to the baking dish, cover with grated mozzarella cheese and add slices of pepperoni on top.
Place in the oven and cook for 25 minutes. Serve immediately.