To begin, cut the boneless chicken breasts into bite-sized pieces.
In a large bowl, marinate the chicken with light soy sauce, vinegar, baking soda, and an egg. Mix well and keep aside for at least 10 minutes.
For dredging, mix together the all-purpose flour and cornflour in a large bowl. Add in the marinated chicken and mix until the pieces are well coated. Dust off the extra flour.
Heat oil for deep frying. Fry the chicken pieces on low heat until cooked and golden. Make sure they do not brown.
To prepare the black pepper sauce - mix together oyster sauce, light soy sauce, vinegar, black pepper, and honey in a large bowl. If you want it spicier, you can add a teaspoon of red chilli flakes.
Heat 2 tbsp of sesame oil in a pan. Add in finely chopped garlic and saute for a minute. Do not brown.
Add in diced onions and diced bell peppers. Cook for a minute or two.
Add in the sauce mix and boil it for 2-3 minutes.
Make a slurry of 1 ½ tbsp cornflour with 3 tbsp of water. Add it to the sauce and cook until it thickens.
Finally, add in the fried chicken pieces and mix until well coated. Add a bit of water if needed.
The Spicy Black Pepper Chicken is ready to serve. Garnish with sesame seeds.