Preheat your oven to 425ºF and grease a 13x9 inch baking pan.
Meanwhile melt butter in a large skillet over medium heat. Add the onions, red bell peppers, green bell peppers, poblano peppers and cook until softened, about 10 minutes. Add in the tomatoes, green chili peppers, garlic, flour, chili powder and salt. Stir the mixture until fragrant and starting to thicken, about 2 minutes.
Add in the stock and heavy cream and bring to a boil. Once boiling, reduce to a simmer and cook 12 minutes, stirring occasionally.
Stir in the sour cream and add the chicken. Season with salt and pepper if needed.
Transfer the mixture to the casserole dish and sprinkle with the cheddar cheese. Arrange the tator tots on top of the cheese. Place the dish in the oven and cook until the tator tots are cooked through and the mixture is hot and bubbling, about 30 minutes. Remove from the oven and let cool 5 minutes before serving.