Combine olive oil and one chopped onion in large saucepan over medium high heat. Cook just until onion is softened about 5 minutes. Add rest of ingredients, turn down heat and simmer while preparing rest of dish.
In another skillet, heat olive oil over medium high heat, add mushrooms, saute until lightly browned. Remove from pan and place in bowl. Saute chopped onion and red pepper until softened, about 5 minutes. Add onion back to skillet, and toss in spinach. Season generously with salt and pepper. Cook for about 2 minutes, or until the spinach starts to lose shape, but is not completely wilted. The spinach will continue to cook in the oven. Remove from heat and set aside.
In a medium size bowl, whisk together the Ricotta cheese, egg, and pesto. Slice the fresh mozzarella and set aside.
Spray a 9x13 pan with Cooking spray. Cover the bottom of the pan with about 3/4 cup of the sauce. Spread around until sauce is covering the bottom of the pan. Place a layer of the lasagna noodles across the pan. Do not overlap the noodles, they will expand when baking. Place the pasta three across. There will be a little gap between the edge of the pasta and the pan. Layer the lasagna as follows:
pasta
1/2 of ricotta mixture
1/3 of remaining sauce
1/2 of vegetable mixture
1/2 of sliced cheese
3 more sheets of pasta
repeat layers and end with sauce layer on top
Cover pan with foil. Place in refrigerator overnight if using next day, or you may freeze at this point. When ready to bake, remove from refrigerator, and let sit on counter for 1/2 to 1 hour. Preheat oven to 350 degrees. Bake for 30 minutes, remove foil. Bake an additional 15 minutes until hot and bubbly. Top with remaining 1 1/2 cups of combined grated Parmesan and mozzarella. Broil or set oven to convection bake until cheese on top is slightly golden.
Remove from oven, and let sit for 15 minutes before slicing.
Notes
-*Sheri uses pesto to give more flavor to the veggie based lasagna. I loved it. She buys the Costco pesto and uses about half of the container, which I love, but didn't have any in my fridge and didn't want to make another trip to COSTCO just for pesto, cause you know then it would have cost me $100 (at least) for that one jar of pesto, bc you can't buy just one item at Costco. Instead, I bought a 7 oz container of Butoni pesto in the refrigerated section at my local grocery.-If you aren't into the no-bake pasta( I like it because it is thinner than the traditional style lasagna that needs boiling) you may use traditional style and boil the pasta. Assemble and bake the same.-If freezing the dish for later baking, cover with plastic wrap and foil. Freeze. Remove from freezer when ready to bake. Remove plastic wrap and replace foil. Bake for about 1 hour 30 minutes. Remove foil about last 30 minutes of baking. Top with last layer of cheese just before broiling.