Season the chicken with salt, pepper, and garlic powder, then toss until evenly coated.
Heat the olive oil in a large skillet, add the chicken, and cook for 7-8 minutes until browned and cooked through. Remove the chicken from the pan and keep warm, or use a separate skillet to cook the vegetables.
Melt the butter in the skillet over medium-high heat. Add the bell pepper, onion, and mushrooms, and cook for 5-6 minutes until they start to soften. Season the mixture with salt and pepper, then add the garlic and cook for about 2 more minutes, until you can smell the garlic and the veggies are cooked.
Add the chicken to the vegetables and mix until combined.
Top the skillet with the sliced cheese, and cover for 1-2 minutes until the cheese has melted.
Scoop the mixture into the rolls and serve.
