Lightly season fillets with salt and cayenne pepper. In large skillet heat oil to moderate temperature. Dredge fish in flour, shake off excess and saute until brown on both sides, about 5-6 minutes. Remove fish from pan, set aside and keep warm.
In clean skillet, melt 1 stick of the butter. Add onions and bell peppers and saute for 3 minutes. Add broth, mushrooms and remainder of butter. Heat through, mixing to incorporate butter. Taste and add more salt and/or cayenne pepper if needed.
Place fillets on plates, divide sauce evenly over top and serve immediately.