Here's a video that shows you how to make it:
1 pound (500 grams) Italian sausage
1 yellow onion, sliced
1½ cups bell peppers, diced
3 cloves garlic, minced
3 cups marinara or pizza sauce
12 lasagna noodles, cooked
6 ounces (180 grams) sliced pepperoni
1 cup basil, packed
3 cups mozzarella
1. Preheat oven to 375ºF/190ºC.
2. Over medium-high heat, cook Italian sausage until browned, then remove from pan and set aside.
3. In the same pan, cook onion until translucent, then add bell peppers and garlic. 4. Cook until the veggies are soft, about 10 minutes. Set aside.
5. In a 9x13-inch baking dish, begin to assemble the lasagna by spreading a thin layer of sauce on the bottom of the pan. Then, layer ingredients in the following order: noodles, ricotta, sausage, veggies, mozzarella, sauce, noodles, ricotta, pepperoni, basil, mozzarella, sauce, noodles, marinara, mozzarella, veggies, sausage, and pepperoni.
6. Place pan on a sheet tray and bake for 45-55 minutes, or until bubbling and starting to brown around the edges.