Preheat your oven to 375°F (190°C).
Season the chicken breast with seasoned salt and black pepper on both sides.
In a skillet over medium-high heat, melt the 1/2 tablespoon of butter. Add the seasoned chicken breast and cook until browned on both sides and cooked through. This usually takes about 4-5 minutes per side, depending on the thickness of the chicken breast. Remove the chicken from the skillet and set it aside.
In the same skillet, add a bit more butter if needed. Add the sliced onions and a pinch of salt. Cook until the onions are softened and golden brown.
Add the sliced mushrooms to the skillet and cook until they are tender.
Place the cooked chicken breast back into the skillet with the onions and mushrooms.
Sprinkle the shredded Monterey Jack cheese over the chicken and vegetable mixture.
Transfer the skillet to the preheated oven and bake for about 10 minutes, or until the cheese is melted and bubbly.
Remove from the oven and let it rest for a few minutes before serving.