1. To make the French onion chicken casserole: Preheat your oven to 400°F (200°C). Lightly grease a 9×12-inch baking dish and set aside.

2. Melt butter in a large skillet over medium-high heat. Add onions and season with salt and pepper. Cook for 5-8 minutes until soft.

3. Reduce heat to medium and cook, stirring occasionally, until onions are caramelized – about 15 minutes. Pour in 1/4 cup of broth to deglaze if your pan gets too dry, and keep stirring until onions are browned. 

4. Stir in fresh minced garlic and cook until fragrant, about 1 minute. Turn off the heat and allow to cool slightly.

5. Season chicken breasts with oregano, crushed chili pepper flakes, salt, pepper, and garlic powder. Go easy on the salt because French onion and cheese are already salted. Arrange chicken breasts in the baking dish. 

6. Divide caramelized onions on top of each chicken breast. Sprinkle shredded cheese on top and bake for 20-25 minutes in the oven (or more, depending on the thickness of your chicken breasts), until fully cooked and cheese is bubbly. Then broil for 2 minutes to crisp up the cheese. Garnish the French onion chicken casserole with fresh chopped parsley and serve immediately with steamed vegetables or cauliflower rice. Enjoy!