Season the chicken with salt, pepper, and garlic powder on both sides.
In a skillet over medium/medium-high heat, add the olive oil.
Add the chicken to the pan and allow to brown until golden on both sides (about 4 minutes per side). Transfer the chicken to a plate (it's okay if it's not completely cooked through; it will continue cooking in the pan later).
Reduce the heat to medium-low. Add the butter and allow to melt. Add the diced onions and cook, while stirring, until the onions soften, about 4 minutes.
Sprinkle in the flour and cook, while stirring, until the flour turns a golden brown, about 1 minute.
Slowly add in the broth, while stirring, and continue stirring until well combined and thickened (make sure to scrape up any brown bits from the bottom of the pan).
Add the chicken back to the pan and continue to gently cook until the gravy has thickened slightly and the chicken cooks all the way through.
Taste and adjust seasoning if needed with salt and pepper.
Serve with mashed potatoes and a green veggie!