Simmer Cashews: Place cashews in a small pot, cover with water, and simmer for 15 minutes. Turn off heat and leave covered.
Make Mushroom Bolognese: Heat oil in a skillet. Sauté onion and garlic for 3-4 minutes, then add mushrooms and bell pepper, cooking until caramelized. Stir in plant protein or lentils, spinach, and marinara sauce. Simmer for 5 minutes and season to taste.
Blend Creamy Marinara Sauce: Add 1 cup marinara, drained cashews, and water to a blender. Blend until creamy, adding salt to taste.
Make Tofu Ricotta: Pulse tofu, salt, olive oil, garlic, nutritional yeast, pepper, and basil/parsley in a food processor until creamy but textured.
Assemble Lasagna: Grease a 9x13-inch baking dish. Layer with marinara sauce, lasagna noodles, mushroom bolognese, tofu ricotta, and basil ribbons. Repeat the layering, finishing with noodles, sauce, and foil.
Bake: Cover tightly with foil and bake at 375°F for 50-60 minutes. Remove foil, test pasta for tenderness, and let stand for 10 minutes.
Serve: Spoon Arugula Pesto on top and sprinkle with basil ribbons.