wash the chicken then pat them dry with a paper towel after that chop into bite-size pieces.
Wash the onion and bell peppers then chop the bell pepper into big pieces and the onion into thin slices.
Prepare three bowls as the following: First one: crack the egg then beat it, Second one: put the cornflour and Third one: mix the flour, salt, paprika, garlic powder and black pepper.
Now, heat the oil in a large or medium skillet on high heat.
After that, coat the chicken pieces in cornflour then dip in the egg and finally coat in the flour mixture then place then in the hot oil and cook for 4-5 minutes on each side (you may need to cook them in two batches).
Then place them on a plate lined with a kitchen towel.
Heat the oil in a large skillet over medium heat then add the onion, bell pepper, ginger and garlic then cook for 2-3 minutes.
After that, add the tomato ketchup, apple cider vinegar, brown sugar, dijon mustard and water and bring to a boil. After that, lower the heat and leave the sauce to simmer until it slightly thickens.
Now, toss the chicken pieces in the sauce, stir to cover the chicken with the sauce then serve.