Meanwhile, rinse lentils and check for little pebbles.
Once you have rinsed the lentils and checked them, add broth and lentils to the skillet. Cover and cook 25-30 minutes or until broth is absorbed and the lentils and tender.
While lentils are cooking, prepare the mashed potatoes. Combine water, milk, butter, salt, 2 minced garlic cloves, and potato flakes in a microwave safe bowl. Microwave, covered, on HIGH for 3 minutes. Remove and stir potatoes with a fork. Set aside.
Add peas, BBQ sauce, and soy sauce to the lentils. Allow to cook for an additional 2 minutes.
Scoop the lentil mixture into an 8x8 casserole dish. Scoop and spread the mashed potatoes over top of the lentil mixture. Bake 12-15 minutes, or until the mashed potatoes are golden on top and pie is bubbling around the edges.
Makes 6 servings. The easiest way to divide into 6 servings is to cut the mashed potatoes into 6 equal sections (I just used a spatula, but you could also use a knife) and then scoop one section onto each plate. For us, one serving was about 1 cup.