Sprinkle steaks with garlic powder, salt, and pepper. Place a large nonstick skillet over medium-high heat until hot. Add steaks; cook 3 minutes on each side or until browned. Remove steaks from skillet, and keep warm.

Increase heat to medium-high; add mushrooms and garlic. Cook, stirring constantly, 5 minutes or until tender. Combine broth, wine, and cornstarch, stirring until smooth. Add to skillet; cook, stirring constantly, 2 minutes or until thickened and bubbly. Return steaks and any steak juices to skillet; cook 2 additional minutes or to desired degree of doneness.

Place 1 slice sourdough toast on each of 4 individual serving plates. Place 1 steak on each piece of toast, and spoon mushroom sauce over steaks.