In a medium bowl, mix the soy sauce, rice vinegar, and cornstarch. Add the chicken pieces and marinate for 10 minutes.
Heat the vegetable oil in a large skillet over medium-high heat. Add the chicken and stir fry until cooked through, about 5-7 minutes. Remove and set aside.
In the same skillet, add garlic and ginger, sauté for about 1 minute until fragrant.
Add the broccoli and red bell pepper, stir-fry until crisp-tender.
Return the chicken to the skillet, add the chili paste, hoisin sauce, sugar, and sesame oil. Stir well to combine and heat through.
Garnish with sliced scallions and serve immediately.
Notes
Adjust the amount of chili paste based on your preferred level of heat.