In a large ziploc bag, whisk together the rice vinegar, soy sauce, mirin, sesame seed oil, garlic, ginger and green onions. Combine the marinade and chicken; marinate around 2 hours, turning the bag occasionally if you remember to.
Drain the chicken from the marinade.
In a bowl, combine the chicken and the flour.
Heat peanut oil in a cast iron skillet to 350 degrees. Add the chicken and fry until golden brown, about 2-3 minutes. Transfer to a paper towel-lined plate.
To make the glaze, combine the rice vinegar, sugar, lemon zest and juice, cornstarch and 2 tablespoons water over medium low heat. Bring to a boil, simmering until thickened, about 1-2 minutes.
Serve the chicken nuggets immediately, tossed or drizzled with the lemon glaze.