Cook lentils in broth or water about 20 minutes until tender.
Sauté onion, carrot, and mushrooms in olive oil until soft.
Add garlic, tomato paste, thyme, paprika, salt, and pepper.
Stir in cooked lentils and peas and add a little broth if needed.
Divide mixture into two small baking dishes.
Boil potatoes until soft, then mash with milk and Greek yogurt.
Spread mashed potatoes over lentil mixture and rough up the top with a fork.
Bake at 375°F for 20–25 minutes until hot. Broil 2 minutes to brown the top if desired.
Let sit 10 minutes before serving.