1. In a large saucepan or pot, heat the oil over medium heat and sauté the onions until translucent. Add the garlic and stir.
2. Add the lentils and water. Bring to a boil and season with the cumin, onion powder, salt, thyme, and pepper.
3. Cover the pot, reduce heat to low, and simmer for 35 minutes. Add the peas and carrots and cook for another 10 minutes. Stir in 2 to 3 tablespoons of mashed potatoes and remove from heat.
4. Preheat oven to 425°F. Transfer the lentil mixture to an 8- x 8-inch baking dish.
5. Serve hot.
6. Gently top with the mashed potatoes. Dot the potatoes with butter and bake at 425° F for 30 to 45 minutes, until most of the liquid is absorbed.