Preheat the oven to 350°F.
Season the chicken lightly with salt and pepper. Bake it for 20 to 25 minutes, until no longer pink in the center.
While the chicken bakes, sauté the peppers, onion, and diced tomatoes with green chiles in a greased skillet until the vegetables are tender. Transfer them to a large bowl.
Let the chicken cool briefly, chop it into bite-size pieces, and add it to the bowl.
Season the chicken and vegetables with 1 tablespoon of taco seasoning.
Add half the shredded cheese, all the cream cheese, and the heavy cream. Stir until combined, then mix in the remaining taco seasoning.
Spread the mixture in a casserole dish, top with the remaining cheese, and bake at 350°F for 30 to 35 minutes.