Prepare the Chicken: Sprinkle salt and pepper generously over both sides of the chicken breasts for seasoning.

Sear the Chicken: Heat 1 tablespoon of olive oil in a large skillet over medium-high heat. Place the chicken breasts in the skillet and cook for 5-6 minutes per side, or until they are golden brown and fully cooked. Transfer the chicken to a plate and set it aside.

Cook the Vegetables: In the same skillet, pour in the remaining tablespoon of olive oil. Add the sliced onion and sauté for 2-3 minutes, or until it starts to soften and become fragrant. Add the garlic, sliced mushrooms, and green beans. Sprinkle with dried thyme and stir well. Cook for an additional 5-6 minutes until the vegetables are tender-crisp and the mushrooms have released their juices.

Add the Broth and Lemon: Pour the chicken broth into the skillet, stirring to scrape up any browned bits from the bottom. Add the lemon juice, if desired, and bring the mixture to a simmer.

Combine and Serve: Return the chicken breasts to the skillet, nestling them among the vegetables. Spoon some of the broth over the chicken and cook for an additional 2-3 minutes to reheat and combine flavors.