I made this for dinner and it is definitely something I'll be adding to my regular menu! 
Ingredients:
Mashed Potato Topping:
3 or 4 medium potatoes, cut into chunks
2 T butter
1/2 cup Greek yogurt
milk
salt and/or other seasonings
Shredded sharp cheddar cheese
Other ingredients:
1 cup cooked lentils (I used green lentils, but brown would be fine.These take about 20 minutes to cook, but could be done earlier in the day or even the day before.)
Veggie bouillon powder
1 cup diced sweet potato
1 cup diced carrots
1 medium onion (cut in chunks)
3 or 4 peeled and coarsely chopped garlic cloves
grape seed oil
salt
thyme
Directions:
Preheat oven to 400 degrees. Toss the sweet potatoes, carrots, onions, and garlic with enough grape seed oil to coat. Spread on a pan and sprinkle with salt and thyme. Roast them until tender (about 30 minutes). 
While the veggies are roasting, start your mashed potato topping. Boil the diced potatoes just until you can put a fork in them. Drain and add the butter and Greek yogurt. Mash the potatoes with a hand masher or a mixer, adding enough milk to make them creamy. I like to add a 1/2 tsp of Wildtree's Onion and Chive seasoning to my potatoes. Set this aside.
Add about 1/2 cup of water and a teaspoon or so of the veggie bouillon powder to the lentils. Transfer the lentils to an oiled casserole dish. Layer the roasted vegetable mixture on the lentils, then add the mashed potato topping over the vegetables. Sprinkle with sharp cheddar cheese (optional).
Bake at 350 degrees until bubbly (about 30 minutes).