Season the chicken on both sides with 1 ½ teaspoons of salt, 1 teaspoon garlic powder, and pepper.
Coat the chicken lightly in flour, tapping off any excess.
Heat the olive oil in a large skillet over medium heat, until shimmering.
Sear the chicken in the hot oil until golden on both sides.
Remove the chicken to a plate and set aside.
Add the butter to the pan, along with the mushrooms, remaining ½ teaspoon of salt and remaining ½ teaspoon of garlic powder.
Saute the mushrooms until softened, then clear out a space in the center of the skillet and add the shallot.
Cook the shallot until tender and translucent, then sprinkle on the flour and stir until the vegetables are coated.
Slowly whisk in the marsala wine.
Whisk in the chicken stock and allow the sauce to come to a simmer and become thick.
Slip the chicken back into the sauce to re-warm.