Place the rice flour on a large plate. Coat the chicken in the flour. Heat a large nonstick skillet over medium-high heat. Add 1 tablespoon of oil and saute half the chicken for 1 to 2 minutes per side until lightly browned. Remove to a plate and keep warm. Repeat with a second tablespoon of the oil and the remaining chicken.
Add the remaining tablespoon oil to the skillet and stir in the mushrooms. Cook for 2 to 3 minutes, until tender. Off heat, add in the marsala and cook for 1 minute, scraping any browned bits from the skillet. Add the broth, salt and pepper. Bring to a simmer and return the chicken and any accumulated juices to skillet. Gently simmer, covered, for 15 minutes.
Meanwhile, prepare couscous following package directions, about 15 minutes.
Stir butter and parsley into the sauce and serve with the cooked couscous.