Preheat oven to 400 degrees. Prepare mashed potatoes according to package instructions and set aside. In a skillet, sauté onions and ground turkey seasoned with garlic powder and salt in olive oil until turkey begins to brown. Layer the bottom of an 8x8 casserole dish with cooked turkey. Add corn to a food processor and pulse until somewhat creamy with some chunks of corn remaining. Place pureed corn over turkey. Top with mashed potatoes. Bake for approximately 25 minutes or until the potatoes begin to brown around the edges.