In a small bowl, combine ½ of the lemon zest and juice with the garlic and rosemary and stir to combine. Place the remaining lemon zest in an airtight container and freeze for future use in marinades, soups, or salad dressings. Reserve the remaining lemon juice and set aside.
Unroll chicken thighs, if necessary, to expose the entire surface area. Season with salt and pepper, if desired.
Place chicken thighs in a large, sealable plastic bag and pour marinade on top. Seal the bag and turn it several times to ensure the chicken is evenly coated. Place the bag in the refrigerator to marinade for at least 30 minutes or overnight.
When ready to cook, heat olive oil in a large skillet over medium-high heat. Remove chicken thighs from the bag, allowing excess marinade to drip off before transferring them to another dish. Discard the remaining marinade.
Working in batches if necessary, add chicken thighs to the hot skillet and cook until browned on each side, approximately 3-4 minutes per side. Transfer thighs to a clean serving platter and set aside.
Add remaining lemon juice and ¼ cup water, if necessary, to a hot skillet to deglaze. Gently scrape the surface of the pan with a spatula to remove any browned bits. Bring liquid to a boil and then reduce heat to medium-low.
Return chicken thighs to skillet and simmer for 3-4 minutes or until chicken is cooked through. Season with additional salt and black pepper, to taste. Remove from heat and serve immediately with your choice of sides.