Pat the chicken cutlets dry with paper towels. Season both sides generously with olive oil, garlic powder, salt, and cracked black pepper.

Heat a large 12-inch oven-safe skillet (cast iron or heavy stainless steel) over medium-high heat. Add the chicken and sear undisturbed for 4 to 5 minutes per side until golden brown and cooked to 160°F (71°C). Transfer chicken to a clean plate and set aside.

Reduce skillet heat to medium. Melt the butter in the same pan, then add the thinly sliced onions and a pinch of salt. Cook, stirring occasionally, for 12 to 15 minutes until deep golden-brown, soft, and sweet. If onions brown too quickly, turn heat down and add 1 tablespoon of water.

Stir in the minced garlic and cook for 1 minute until fragrant. Sprinkle flour over the onions and stir well to coat for 1 minute.

Pour in the dry white wine to deglaze the skillet, scraping up all the savory browned bits from the bottom. Simmer for 2 minutes until liquid reduces by half.

Pour in the beef broth, Worcestershire sauce, and fresh thyme leaves. Bring to a gentle simmer for 3 to 4 minutes until the sauce slightly thickens into a rich, glossy onion gravy.

Nestle the seared chicken cutlets back into the bubbling onion gravy. Spoon some of the caramelized onions over the top of each piece.

Blanket each chicken cutlet generously with the shredded Gruyère and Swiss cheese blend.

Transfer skillet to oven and broil on HIGH for 2 to 3 minutes (or cover with a lid on the stovetop for 3 to 4 minutes) until the cheese is completely melted, bubbly, and toasted golden brown.

Garnish with fresh thyme leaves and cracked black pepper. Serve hot straight from the skillet over garlic mashed potatoes or with crusty French bread.