Preheat oven to 350 degrees F.
Spray a large skillet with cooking spray and add the green peppers, red peppers and onion. Cook over medium heat for 5 minutes.
In a large bowl mix together the cream cheese, diced tomatoes, salt and fajita seasoning.
In a small bowl mix together the mozzarella cheese and Mexican cheese.
Add the chicken, peppers, onions and half of the shredded cheese to the cream cheese mixture. Stir together.
Spray a 2 quart casserole dish with cooking spray and add the chicken mixture. Top with the remaining shredded cheese.
Bake 25 minutes or until it is heated through and the cheese is melted.