I found this on another recipe site and tweaked it a little. We ate it last night with super fresh mozzarella and LOVED it. We made some garlic mashed potatoes to go with it and also added some fresh mozzarella to the mashed. Excellent dinner.
Heat the olive oil in a skillet over medium heat. Place chicken in the skillet, and season with garlic powder and onion powder. Cook until juices run clear. Set chicken aside, and keep warm.
Stir mushrooms and onions into the skillet, and cook until tender. Return chicken to skillet, layer with mushroom and onions, and top with cheese. Cover skillet, and continue cooking 5 minutes, or until cheese is melted.