(against the grain) into very thin slices; sprinkle with 1/4 teaspoon each salt and pepper. In 12" nonstick skillet over medium-high heat, heat 2 teaspoons iol; add beef; cook and stir 2 to 3 minutes until bronwed. Using slotted spoon, remove beef to plate. In same skillet over medium-high heat, heat remaining 1 teaspoon oil; add garlic; cook and stir 30 to 60 seconds until fragrant. Add frozen vegetables, 1/4 cup water, and remaining 1/4 teaspoon each salt and pepper; cook, covered, 3 minutes until tender. Meanwhile, in small bowl stir peanut butter and remaining 1/2 cup water to blend; add to skillet along with beef and any accumulated juices. Cook, stirring 1 to 2 minutes longer until heated through and coated with sauce.