Add salt and pepper to both sides of the chicken to season it. Place ⅓ cup of flour in a shallow bowl and dredge the chicken in it so that it is covered in flour.
Place 2 tablespoons of olive oil in a large skillet and heat over medium-high. Add the chicken and sear it on both sides until it turns golden brown and crispy. It should take between 3-5 minutes on each side.
Add the butter to the skillet and continue to brown the meat for another 1 minute. Remove the chicken using a slotted spoon.
Pour the remaining olive oil into the skillet with the mushrooms. Cook until they become soft, about 5 minutes.
Add the remaining 3 tablespoons of flour to the pan with the mushrooms and toss to coat them completely. Pour in the chicken broth and whisk to combine.
Whisk in the heavy cream and onion powder. Taste and season with salt and pepper if needed. Bring the mixture to a simmer, then reduce the heat the low. Allow it to cook for 10 minutes.
Place the chicken back in the skillet and allow it to simmer for 5 more minutes. Use a food-safe thermometer to make sure that the chicken has an internal temperature of 165°F.
Remove the chicken from the skillet and serve over mashed potatoes, pasta, or rice. Spoon the sauce on top and enjoy!