Preheat the oven to 375°. Spray a 13x9 inch casserole dish with cooking spray.
In a skillet, brown the ground beef or turkey over medium-high heat. Drain the fat if there is excess. Add the onion and saute until tender. Place this mixture in the casserole dish.
In the skillet, melt the margarine. Sprinkle the flour over it and whisk together for about 1 minute. Whisk in half of the broth. Allow mixture to bubble and thicken and add more broth until the mixture is the consistency of thick gravy.
Pour the cream sauce mixture over the beef/turkey mixture in the casserole dish and mix together. Next, cover beef/turkey mixture with frozen mixed vegetables. Then, top with enough tater tots to cover the entire vegetable layer.
Bake at 375 degrees for 45 minutes. Remove the cover and bake an additional 15 minutes at 425 degrees or until the tater tots are golden brown and crispy. Serve immediately.
See the notes in the post about finding allergy friendly tater tots.
Read labels carefully to make sure ingredients do not contain your allergens.