Season the chicken with salt and pepper, then dust with flour.
Heat the oil in a large skillet 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, cooking for 3 minutes until the garlic is lightly browned. Transfer the chicken to a platter.
Add the stock to the skillet, cooking over high heat and scraping up browned bits until reduced by half, about 5 minutes.
Add the lemon juice and butter, swirling until emulsified.
Return the chicken and 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.