Preheat oven to 425°F. Bake potatoes according to package instructions. Microwave chicken according to package instructions and cut into bite-size pieces.
In a medium bowl, mix together tomato sauce and seasoning mix. In another medium bowl, combine tomatoes, pepper, onion and 1 Tbsp. of sauce mixture.
Arrange Tater Tots on oven-safe serving platter. Sprinkle cheese over top and bake for 2 to 3 minutes, or until cheese is melted. Spoon tomato mixture on and top with chicken. Drizzle with remaining sauce mixture. Garnish with sliced avocado if desired.