Heat the olive oil in a large skillet over medium high heat. Season the chicken with salt and pepper. Place the flour in a shallow dish and dredge the chicken through it, coating the chicken on both sides. Place the chicken in the hot skillet and brown until golden brown and crusty, about 4 minutes per side. Transfer the chicken to a plate.
Add the mushrooms (or other vegetables) to the pan and cook, stirring often, until they are softened and starting to brown, about 5 minutes.
Deglaze the pan with the chicken stock and lemon juice, using a wooden spoon to stir and scrape up any browned bits from the pan bottom.
Stir in the butter until it is melted, then add the chicken back to the sauce. Top with chopped parsley or other herbs, if desired, and serve with lemon wedges (for those who want a tangier dish).