Remove any visible fat from the chicken. Cut the chicken into bite sizes.
Season the chicken with salt, black pepper, garlic, ginger, and mirin. Let it rest for 30 minutes.
Heat a large non-stick skillet over medium high heat and pour about 1 inch of oil. When the oil is hot enough, coat a piece of chicken with starch evenly and slide the coated chicken piece into the hot oil. Repeat until every chicken pieces are placed in the hot oil. Cook until light golden brown, turning over a few times with tongs.
Remove from oil and set them on a cooling rack. Turn off the heat, and let the chicken cool down for a few minutes.
Reheat the oil and fry the chicken again until they are golden brown and crispy. Remove from oil and set them on a cooling rack. Turn off the heat, and let the chicken cool down for a few minutes.
Gochujang Sauce
In a small bowl, mix all the sauce ingredients until well combined.
Remove oil from the skillet. Heat the mixed sauce with low heat until it starts to bubble. Simmer until it thickens slightly. Add the fried chicken into the sauce and stir well until every pieces are evenly coated.
Remove from the heat and transfer the coated chicken to a large platter. Sprinkle the peanuts on top.