Preheat your oven to 350°F.
Heat the oil in a large oven proof dutch oven or pot over medium low heat.
Add the mushrooms and onions, and cook until onions are soft and mushrooms have browned.
Add the garlic and cook for about two to three minutes more. Remove from heat.
In a large bowl, add your lentils, rice, and mushroom mixture. To that add your basil, oregano, fennel, and half the jar of marinara. Stir and combine well. Season to taste with salt and pepper.
In the pot you used to cook the onions and mushrooms, spread a thin layer of the marinara sauce on the bottom of the pan
Fill each pepper with your lentil mixture, then place into your pot. Top each pepper with a scoop of marinara and a pinch or two of vegan mozzarella if you’d like. Put the lid on the pot, and bake in your preheated oven for 1/2 hour.
Remove the lid from the pot, and cook for about 10 more minutes. Remove from the oven, let cool ten minutes, then serve!