Preheat the oven to 350°F.
Prepare the lasagna noodles as needed (see notes).
Chop the bell pepper, zucchini, and mushrooms.
In the large, deep pan over medium heat, add olive oil and sauté the garlic and onion for a three minutes until fragrant. Then, add the ground beef and break up into small pieces. Once fully cooked, transfer to a plate and drain most of the excess grease.
In in the same pan over medium heat, add more olive oil if necessary, then sauté the bell pepper. Cook for five minutes before adding the zucchini and mushrooms.
When the vegetables are starting to get soft, turn off heat and stir in the cooked beef. Pour in the marinara sauce and incorporate everything together.
Lightly coat the bottom of a 9x13 baking dish with spoonfuls of the marinara mixture. Add a layer of lasagna noodles. Then spread about 1/3 of the dairy free ricotta onto the noodles, followed by about a 1 and 1/2 cup of the meat and veggie sauce.
Repeat the layering process 3 times, finishing with a layer of sauce. Cover the dish with foil.
Bake for about 40 minutes. Remove the foil, sprinkle on the dairy free mozzarella (see notes) and bake uncovered for another 10 minutes.
Remove from the oven and allow about 10 minutes to cool before enjoying!