Preheat oven to 350 F.
Place 1 tablespoon of olive oil in a large saute pan over medium heat and cook the onions for 2 minutes.
Add the mushrooms, season with 1/2 teaspoon of salt, and cook another 4 minutes or until the mushrooms are tender and the onions are translucent.
Remove the mushroom mixture from heat and place in a bowl.
Heat 1 teaspoon of oil in the sauté pan and cook the chicken, garlic powder and remaining 1/2 teaspoon of salt for 3 minutes or until cooked through.
Combine all the ingredients together, place in an 8 x 8 inch baking dish, and sprinkle with additional shredded cheese. Bake for 20 minutes. Serve.