Make marinade: combine soy sauce, mirin, 1 tbsp lemon juice, 2 tbsp corn flour and chicken in a bowl. Toss/stir to coat the chicken and refrigerate minimum 30 minutes
Make sauce: combine water, 3 tbsp lemon juice, raw sugar and 2 tbsp corn flour in a bowl, set aside while cooking the chicken
Heat oil in frypan on high heat, add chicken and cook until crispy and cooked through, remove from pan and drain on paper towel
Add sauce to pan and cook until starting to bubble and hot, return chicken to pan and stir through to coat in sauce. Sauce will continue to thicken as it cools
Put on a serving plate and sprinkle with sesame seeds, then serve immediately while hot