Prepare the Chicken: Pat chicken breasts dry and season both sides with garlic powder, onion powder, paprika, salt, and pepper.
Cook the Chicken: Heat olive oil in a grill pan over medium-high heat. Grill each breast for about 5–6 minutes per side, or until fully cooked (internal temperature reaches 165°F / 74°C). Remove from pan and keep warm.
Sauté the Vegetables: In a separate skillet, melt butter. Add sliced onions and mushrooms, cooking until softened and golden brown (about 5–7 minutes). Add a splash of chicken broth if needed for extra flavor.
Assemble the Dish: Place cooked chicken breasts on a baking sheet or oven-safe dish. Top each with sautéed onions and mushrooms, then sprinkle shredded cheese generously on top.
Melt the Cheese: Broil or bake for 2–3 minutes; just until the cheese melts and becomes bubbly.
Serve: Plate immediately and serve with your favorite sides like mashed potatoes, rice, or steamed vegetables.