In a 12” nonstick skillet, melt butter over medium-high heat. Cook bell pepper in butter 2 minutes, stirring frequently. Stir in mushrooms. Cook 2-3 minutes, stirring frequently, until vegetables are tender.
Remove vegetable mixture from skillet; cover to keep warm.
Sprinkle beef steaks with garlic salt and pepper. In same skillet, cook steaks over medium heat 6-8 minutes, turning once or twice, until desired doneness.
Return vegetables to skillet. Stir teriyaki glaze and water into vegetables and spoon over steaks. Cook about 1 minute, stirring vegetables occasionally, until thoroughly heated.