Add oil to deep-sided large skillet or pan and set heat to medium high. Brown ground beef and sausage together.
Add pepperoni, tomatoes, tomato paste, oregano, salt, pepper, garlic, red pepper flakes, onion, and water to pan. Reduce heat to low and simmer to 30 minutes.
Preheat the oven to 350 degrees ˚. Cook the lasagna noodles according to the package directions and drain.
Spread sauce on bottom of a 9×13 baking pan or casserole dish. Layer noodles, ricotta, mozzarella, and parmesan. Repeat process starting with sauce, then noodles, and ending with cheeses.
Bake 40 minutes or until cheese is melted and sauce is bubbling. Allow to cool for 15 minutes before serving.