Rinse steaks thoroughly in cold water, and sprinkle with salt and pepper; set aside.
Sauté garlic in butter in a large skillet until tender; add lemon juice and steaks to skillet. Cook over medium heat, turning steaks once, until fish flakes easily when tested with a fork. Transfer fish to a warm serving platter. Reserve drippings in skillet.
Sauté mushrooms in skillet until tender. Add chicken broth, soy sauce, and cornstarch. Cook over medium heat, stirring constantly, until sauce thickens.
Spoon sauce over steak. Serve immediately with hot cooked rice.