Heat olive oil in a large heavy-bottomed skillet over medium-high heat.
Add thinly sliced chicken to the skillet and sear until browned and cooked through, roughly 5 to 7 minutes.
Remove chicken from the skillet and set aside on a plate.
Add onions, bell peppers, and mushrooms to the same skillet, sautéing for 6 to 8 minutes until vegetables are tender-crisp.
Return the chicken to the skillet and toss with the vegetables to incorporate.
Season the mixture with salt, black pepper, and garlic powder.
Reduce heat to low and arrange provolone cheese slices evenly over the top of the chicken and vegetable mixture.
Cover the skillet with a lid for 1 to 2 minutes until the cheese is fully melted and bubbly.
Remove from heat and serve immediately.