Prepare the chicken by seasoning the breasts generously with salt and black pepper on both sides.
In a large skillet, heat the olive oil over medium-high heat and sear the chicken breasts for about 5-7 minutes on each side until golden brown and cooked through.
Transfer the chicken to a plate and cover to keep warm. In the same skillet, reduce heat to medium and sauté the diced onion for 2-3 minutes until translucent.
Add the minced garlic and chopped rosemary, cooking for an additional minute until fragrant.
Zest one lemon and add the zest to the skillet, then squeeze the juice of both lemons into the pan along with the chicken broth.
Scrape up any browned bits from the bottom of the pan to enhance the sauce.
