Whisk first 5 ingredients until blended. Toss chicken with garlic salt and pepper.
In a large cast-iron or other heavy skillet, heat 1 tablespoon oil over medium-high heat; stir-fry chicken until no longer pink, 3-4 minutes. Remove from pan; keep warm.
In same pan, heat remaining oil over medium-high heat; stir-fry coleslaw mix, onion and ginger until broccoli is crisp-tender, 2-3 minutes. Stir in peanut butter mixture. Serve chicken and vegetable mixture in tortillas.
