Season the chicken with salt and pepper and dust with flour. In a large skillet, heat the oil until shimmering. Add the chicken and cook over high heat, turning once, until browned and crusty on both sides, about 10 minutes. Add the garlic and rosemary and cook for 3 minutes, until the garlic is lightly browned. Transfer the chicken to a platter, leaving the rosemary and garlic in the skillet.
Add the stock to the skillet and cook over high heat, scraping up any browned bits, until reduced by half, about 5 minutes. Add the lemon juice and butter and swirl until emulsified. Return the chicken and any accumulated juices to the skillet. Add the peppers and cook, turning the chicken until coated in the sauce, about 3 minutes. Transfer the chicken and sauce to the platter and serve.