Preheat oven to 350 degrees.
Lightly-coat a 13 x 9 inch pan with cooking spray. Set aside.
Meanwhile, heat a large skillet over medium heat.
Cook ground beef, pork and sausage until no longer pink. Drain and put into a large bowl.
Fry chopped bacon until cooked, almost crisp. Drain on paper towel.
Add ½ of the bacon to large bowl with ground meat in it.
Sauté onions, mushrooms and peppers until tender. Add some butter if needed in the pan. Dump in large bowl as well.
Prepare pasta according to package directions. Drain and add to large bowl.
Add tomato sauce, canned, diced tomatoes, Italian seasoning, salt, pepper, ½ cup of cheese, ham or pancetta and half of the pepperoni to that large bowl and stir until combined.
Put contents of the bowl into prepared pan and spread as evenly as possible.
Sprinkle remaining half of bacon and crispy fried onions all over the meat and pasta mixture.
Sprinkle remaining shredded cheese all over top of the crispy fried onions.
Sprinkle Parmesan cheese on top.
Lastly, place pepperoni slices across top of cheeses.
Bake for 45 minutes.
Then turn the oven up to broil and bake until cheese is brown and pepperoni edges start to darken.
Remove from oven and let stand for at least 10 minutes before serving. Enjoy!