Boil spaghetti in salted water according to package directions until al dente, then drain thoroughly.
Heat large skillet over medium-high heat and sauté ground beef with diced red onion, sliced mushrooms, and diced bell pepper until beef is browned and vegetables are soft. Drain excess fat.
Add Italian seasoning, onion powder, garlic powder, and seasoned salt to the skillet and stir to evenly coat meat and vegetables.
Stir in pepperoni slices, most of the bacon crumbles, pizza sauce, and pasta sauce. Let simmer gently for 3 to 5 minutes.
Add drained spaghetti to the skillet and toss well to combine with sauce, meat, and vegetables.
Transfer mixture into a baking dish and sprinkle shredded mozzarella cheese evenly over the top. Garnish with remaining bacon, diced onion, sliced black olives, diced bell pepper, and remaining pepperoni.
Bake in a preheated oven at 175°C (350°F) for 10 minutes, then broil for an additional 2 to 3 minutes until cheese is bubbly and golden.
Remove from oven and serve warm.