Drizzle the olive oil into a large pot over medium-high heat. Add the sausage, ground beef and pepperoni and stir, breaking the meat up as it begins to cook. Continue cooking, stirring occasionally, until brown, and then remove the meat to a plate.
Add the mushrooms, garlic, bell peppers and onions to the pot and saute until the mushrooms have softened and the others have some color. Add the meat back in along with the tomatoes, tomato paste, pesto, half the parsley, 1 teaspoon of the salt, 1/2 teaspoon of the black pepper and the crushed red pepper flakes. Stir, reduce the heat to low and simmer for 25 to 30 minutes. Add the black olives and stir.
Preheat the oven to 350 degrees F.
To make the cheese mixture: Combine the ricotta and eggs in a large bowl. Add the Parmesan, the rest of the parsley and the remaining 1 teaspoon salt and 1/2 teaspoon pepper. Stir the mixture until totally combined.
To assemble the lasagna: Overlap 4 lasagna noodles in the bottom of a large rectangular baking dish. Spoon half the cheese mixture over the noodles and smooth it out into a flat layer. Lay half of the mozzarella slices on top followed by half of the meat sauce. Repeat these layers once more and top with some extra Parmesan. Bake until heated through and bubbly on the top, 40 to 45 minutes.
The lasagna can be made up to 2 days ahead of time and stored in the fridge, unbaked. It can also be frozen, unbaked. Just thaw before you're ready to bake it.
Recipe courtesy of Ree Drummond