In a medium bowl, toss the chicken with cornstarch, soy sauce, rice vinegar, and sesame oil. Let marinate for 15 minutes.
Heat 1 tablespoon vegetable oil in a large skillet or wok over medium-high heat. Add the chicken and cook until browned and cooked through, about 5-7 minutes. Remove chicken from the skillet and set aside.
Add the remaining 1 tablespoon vegetable oil to the skillet. Add the red bell pepper, green bell pepper, and onion. Cook until softened, about 3-5 minutes.
Add the minced garlic and grated ginger to the skillet. Cook for 1 minute until fragrant.
Stir in the chicken broth, chili garlic sauce, brown sugar, and crushed Szechuan peppercorns (if using). Bring to a simmer.
Return the cooked chicken to the skillet and toss to coat with the sauce. Cook for 2-3 minutes, allowing the sauce to thicken slightly.
Garnish with chopped green onions and serve hot over cooked rice.
Notes
Adjust the amount of chili garlic sauce to your preferred spice level.
For extra crunch, you can add some chopped peanuts or cashews at the end.
If you don’t have Szechuan peppercorns, you can omit them, but they add a unique flavor.