Pat the boneless chicken dry with paper towels and dice it in to bite sized chunks. Season with a little salt and pepper.
Heat the olive oil in a large dark skillet and brown the chicken chunks in the hot skillet in batches until they have a little sear on them.
In a bowl, whisk together the soy sauce, sugar, vinegar, ginger, garlic and pepper until the sugar has dissolved.
Return all the chicken to the skillet and pour the sauce over the top. Simmer in the sauce about 8-10 minutes until it is cooked through, then stir in the cornstarch mixture a little at a time until the sauce is the consistency you like! (The more of the mixture you add, the thicker it will become.)
Let simmer another minute or two, then remove from heat and serve over rice!