Step 1: Preheat your oven to 375°F (190°C). In a large, oven-safe skillet or Dutch oven (or a large pot for browning, then transfer to a 9×13 inch baking dish), heat the olive oil over medium-high heat. Add the crumbled Italian sausage and ground beef. Break up the meat with a spoon as it cooks. Cook until thoroughly browned, about 8-10 minutes. Drain any excess grease, leaving about 1-2 tablespoons in the pan.
Step 2: Reduce the heat to medium. Add the diced onion and bell pepper to the skillet with the browned meats. Sauté until softened, about 5-7 minutes. Add the minced garlic, dried oregano, dried basil, and red pepper flakes (if using). Cook for another minute until fragrant, stirring constantly.
Step 3: Pour in the marinara sauce and water or beef broth. Bring the mixture to a gentle simmer, then reduce heat to low, cover, and let it cook for at least 15-20 minutes, allowing the flavors to meld. Season with salt and black pepper to taste.
Step 4: While the sauce simmers, bring a large pot of salted water to a rolling boil. Add the pasta and cook according to package directions until al dente (firm to the bite). Drain well.
Step 5: Add the drained pasta to the skillet with the sauce and meat mixture. Stir to combine thoroughly, ensuring every piece of pasta is coated. Spread half of the pasta mixture evenly in the bottom of your oven-safe skillet or 9×13 inch baking dish. Layer with half of the pepperoni slices and half of the shredded mozzarella and provolone cheese blend.
Step 6: Top with the remaining pasta mixture, then layer with the remaining pepperoni slices and the rest of the cheese blend.
Step 7: Cover the skillet or baking dish with aluminum foil. Bake for 20 minutes. Then, remove the foil and continue baking for another 15-20 minutes, or until the cheese is melted, bubbly, and lightly golden brown, and the edges are simmering. If desired, you can broil for the last 2-3 minutes for an extra crispy top (watch carefully to prevent burning).
Step 8: Let the Meat Lovers Pizza Pasta Bake rest for 10 minutes before serving. This allows the casserole to set and prevents it from falling apart when scooped.