Preheat oven to 375°F. Prepare loaf pan with vegetable pan spray.
In large skillet, heat olive oil over medium heat. Add onion; cook, stirring occasionally until soft and translucent, about 6-8 minutes. Stir in salt, pepper and garlic powder. Cool slightly.
In large bowl, gently combine cooked onions, beef, 1 cup tomato sauce, breadcrumbs, and eggs, mixing until well combined. Press evenly into baking pan.
Bake 60-70 minutes or until thermometer inserted in center of meatloaf reads 150°F. Pour remaining sauce over meatloaf. Cook an additional 15 minutes or until thermometer reads 160°F. Cool 10 minutes before slicing and serving.