Start by patting the boneless skinless chicken breasts dry with paper towels, then season generously with kosher salt and black pepper, and cut the chicken into 1-inch pieces.

In a large skillet, heat olive oil over medium-low heat. Add the sliced yellow onions, and sauté gently while stirring occasionally for about 20 minutes until softened and caramelized. Stir in minced garlic for the last minute.

In a bowl, mix all-purpose flour, dried oregano, salt, and pepper. Dredge chicken pieces in the mixture for even coating. Return the skillet to medium-high heat and add chicken, sautéing for about 6 minutes until golden brown.

Pour in beef broth and add caramelized onions back into the skillet. Bring to a gentle boil, then lower to a simmer for about 12 minutes, ensuring chicken is fully cooked to an internal temperature of 165°F.

While chicken simmers, bring salted water to a boil, add pappardelle or wide egg noodles, and cook until al dente. Drain, toss with butter for a creamy texture.

Remove the skillet from heat and sprinkle shredded Gruyère cheese over the mixture. Cover for a couple of minutes to allow cheese to melt, then serve over buttered pasta and garnish with fresh parsley.