Tear protein into 1" chunks. Toss protein in batches with cornstarch, tapping off the excess. Set dredged ch'kn on a platter and set aside.
In a separate dish, combine all the ingredients for your sauce and whisk to combine.
Preheat a non-stick skillet with oil. Cook ch'kn in 2 to 3 batches, sauteeing until golden on both sides and cooked through then remove the ch'kn from the pan and transfer to a bowl. Repeat with the remaining ch'kn, adding more oil as needed. Leave at least 1 Tbsp oil in the pan.
Add the garlic, ginger and pepper flakes. Sautee for about 30 seconds or until fragrant.
Add the sauce to the skillet and bring it to a simmer while stirring. Let it simmer for 1 minute to cook off the vinegar a little. Taste the sauce and add more soy sauce or rice vinegar to taste if desired. Add the ch'kn and toss to coat. Serve garnished with sesame seeds if desired.
