Preheat oven to 375 degrees
Prepare the peppers by cutting off the top, remove the ribs and seeds and cut in half lengthwise. Prick the peppers with a knife several times and lay them on a baking dish or roasting pan.
In a large skillet, saute onions in olive oil until tender then stir in the garlic until fragrant.
Stir in the lentils, seasonings, 1 ½ cups of the marinara and the vegetable broth and bring to a simmer.
Stir in the rice, salt and pepper and half of the cheese. When the mixture is well heated, spoon into the prepared peppers.
Top the peppers with the remaining sauce and add ½ cup of water to the pan. This will help the peppers to cook through.
Cover loosly with foil and bake for 45-50 minutes.
Top the peppers with the remaining cheese and bake for 5-10 minutes more until the cheese is melted and starts to brown. Season with salt and pepper if necessary.