In medium bowl, whisk together vinegar and sesame oil. Add onions and 2 cups shredded coleslaw veggie mix; toss to combine. Refrigerate until ready to use.
Meanwhile, In large skillet, heat olive oil over medium-high heat. Add chicken and bell pepper; cook 6 to 8 minutes or until chicken is cooked through, breaking up chicken with side of spoon as it cooks. Add garlic, tomato paste and ginger; cook 1 minute, stirring constantly.
Stir in water, hoisin sauce, soy sauce, sriracha and remaining 2 cups shredded coleslaw veggie mix; heat to boiling. Reduce heat to medium-low; simmer 4 to 5 minutes or until mixture is thickened, stirring occasionally.
Divide sloppy mixture between buns; top with coleslaw.
