Lentil and mushroom shepherd's pie is a vegetarian twist on a classic dish. Start by sautéing onions, garlic, and mushrooms in a pot until they are soft. Add in cooked lentils, vegetable broth, and your favorite seasonings. Let the mixture simmer for about 10 minutes. Top with mashed potatoes and bake in the oven for about 30 minutes until the potatoes are golden brown. Serve with a side salad for a filling and satisfying meal.