Season Chicken breasts with Salt and Black pepper.
Heat Olive oil in a large skillet over medium-high heat. Add Portobello mushrooms and Onion and cook until softened and browned, about 5-7 minutes. Remove from skillet and set aside.
In the same skillet, melt Butter. Add Garlic and cook for 1 minute until fragrant.
Pour in Chicken broth and Worcestershire sauce. Bring to a simmer and cook for 5 minutes, reducing slightly.
Stir in Lemon juice.
Add Chicken breasts to the skillet and cook for 6-8 minutes per side, or until cooked through.
Top each Chicken breast with the cooked Mushroom mixture and shredded Monterey Jack cheese.
Cover the skillet and cook until the cheese is melted, about 2-3 minutes.
