Combine all ingredients in a small bowl. Set aside.

Toss chicken cubes with cornstarch, salt, and pepper until coated.

Heat a thin layer of oil in a large, deep frying pan or wok over high heat. Add chicken and sear for about one minute per side, until starting to brown. Remove chicken from pan and set aside. If necessary, work in batches to avoid overcrowding the pan.

Reduce heat to medium. Add sesame oil, garlic, and ginger. Cook, stirring the entire time, for about a minute, until the garlic and ginger start to brown.

Add sliced onion and stir well. Increase heat to medium-high and stir-fry for about five minutes, until onions are translucent. Add pastrami and stir-fry for an additional few minutes.

Increase heat to high and add snow peas. Stir-fry for one minute, then add chicken and sauce. Stir well to incorporate and continue to cook until the sauce starts to bubble. If necessary, reduce heat to low and cook just until the chicken is cooked through.