We love that this recipe comes together in one skillet and in less than an hour, meaning it's WAY faster than French Onion Soup. Dunking good bread into the extra pan sauce is highly encouraged.
3 tbsp. extra-virgin olive oil, divided1 Large onion halved and thinly sliced2 tsp. freshly chopped thymeKosher saltFreshly ground black pepper2 cloves garlic, minced1 3/4 lb. boneless skinless chicken breasts, cut into 1" pieces1/2 tsp. dried oregano2 tbsp. all-purpose flour1 1/2 c. low-sodium beef broth1 c. shredded GruyèreFreshly chopped parsley, for garnish
In a large skillet over medium heat, heat 2 tablespoons oil. Add onions and season with salt, pepper, and thyme. Reduce heat to medium-low and cook, stirring occasionally until onions are caramelized and jammy, about 25 minutes. Stir in garlic and cook until fragrant, 1 minute more. Turn off heat and remove onion mixture. Wipe skillet clean.
In a large bowl, season chicken with salt, pepper, and oregano, then toss with flour. Heat remaining oil in the same skillet over medium-high heat. Add chicken and cook until golden on all sides and mostly cooked through, about 8 minutes.
Add beef broth and return caramelized onions to skillet. Bring mixture to a boil, then reduce heat and simmer until chicken is cooked through and beef broth reduces slightly about 10 more minutes.
Add Gruyère and cover skillet with a lid. Cook until cheese is melty, about 2 minutes. Remove from heat and garnish with parsley before serving.