1. In a large skillet, stir-fry potatoes in butter and oil for 8-10 minutes or until lightly browned.
2. Meanwhile, place flour in a large resealable plastic bag. Add fish, a few pieces at a time, and shake to coat. Add to the skillet. Cover and cook for 4 minutes, stirring occasionally.
3. Add the mushrooms, celery, onion and garlic. Cover and cook 4-6 minutes longer or until fish flakes easily with a fork. Sprinkle with lemon juice, salt and pepper. Yield: 4 servings.