Preheat the oven to 350*.
Sauté onions and mushrooms until onions are translucent mushrooms are browned.
Put the chicken stock and cream cheese in a bowl and microwave for a minute to melt the cream cheese. Whisk in the dressing mix, garlic powder, and black pepper into the cream cheese mixture until smooth. Stir in the tomatoes, artichokes, mushrooms, and onions.
Place the chicken breasts into a casserole dish. Pour the cream cheese mixture over the chicken. Bake for 30 to 40 minutes or until the chicken is done. Sprinkle the shredded cheese over the top and stick it under the broiler for a few minutes to melt the cheese.
Voila! Cheesy, melty, keto-fied goodness. All in one casserole dish!