Make black pepper sauce by whisking together black pepper, rice vinegar, light soy sauce, dark soy sauce, brown sugar, toasted sesame oil, cornstarch, and water in bowl until no lumps remain. Set aside.

Coat chicken with 1 tablespoon of sauce, 2 tablespoons cornstarch, and salt. Let rest while preparing vegetables to help coating adhere.

Heat large frying pan or wok until very hot. Add 1 tablespoon oil and tilt pan to spread. Add chicken in single layer and cook over medium heat until golden on bottom. Flip and cook until chicken begins to brown and is almost cooked through. Transfer to plate.

Heat remaining tablespoon oil in same pan. Add ginger, garlic, and chopped chilies. Sauté for 30 seconds until fragrant.

Immediately add onion and bell peppers. Stir fry over high heat for 2-3 minutes until vegetables are crisp-tender with some char on edges.

Reduce heat to low. Whisk sauce to recombine as cornstarch settles, then pour into pan. Let simmer for 30 seconds until sauce thickens and becomes glossy.

Add cooked chicken back to pan and toss well until chicken is warmed through and coated in sauce. Switch off heat and add freshly ground black pepper. Stir to combine and serve hot over rice.