Pat the chicken thighs dry with a paper towel to remove excess moisture, ensuring proper browning.
Combine onion powder, paprika, salt, and pepper in a small bowl.
Generously rub the chicken thighs with the seasoning mixture and set aside.
Place green beans in a microwave-safe dish with 1/2 cup water and microwave for 8-10 minutes until almost done but still crisp.
Melt 2 tablespoons of butter in a large cast-iron skillet over medium-low heat.
Cook the chicken thighs top side down until golden, about 5-6 minutes, then flip and cook for another 5-6 minutes or until a thermometer shows 165°F (75°C).
In the same skillet, melt the remaining butter, add garlic, parsley, hot sauce, chili flakes, and pre-cooked green beans. Cook for 4-5 minutes.
Add lemon juice and chicken stock, reduce for a couple of minutes until sauce thickens.
Reintroduce the chicken to the skillet, adjust seasoning, and quickly reheat.
Serve warm, garnished with chili flakes, parsley, and a lemon slice.