Preheat the Oven: Preheat your oven to 375°F. Meanwhile, prepare all the ingredients so that everything is ready to go.
Cook the Meat: In a large skillet, heat the olive oil over medium heat. Add the chopped onions and garlic powder; cook until soft. Then, add the ground turkey. Stir well and season with salt, pepper, and onion powder. Cook until the turkey is browned and crumbled.
Add Veggies: Once the meat is cooked, stir in the diced tomatoes and optional bell peppers. Let the mixture simmer for about 5 minutes so that the flavors meld together. If you like a bit of crisp texture, add the shredded lettuce just before moving on to the next step.
Prepare the Sauce: In a small bowl, combine the Greek yogurt, ketchup, and mustard. Mix until smooth. This tangy sauce will bring the layers of flavor together without needing alcohol-based ingredients.
Assemble the Casserole: In a large casserole dish, spread a thin layer of the turkey and vegetable mix on the bottom. Then, arrange a single layer of frozen tater tots over the mixture. Next, drizzle some of the homemade sauce evenly on top. Repeat layering until all ingredients are used, finishing with a layer of tater tots on top. Sprinkle the shredded low-fat cheese over the final layer.
Bake: Place the casserole in your heated oven and let it bake for 35 to 40 minutes. During the last 10 minutes, check to ensure the cheese is melted and the tater tots are golden brown and crispy.
Serve and Enjoy: Once baked, remove the casserole from the oven and let it cool for a few minutes. Serve warm and enjoy a comforting, unique twist on a fast-food classic.