Put Panko in a large bowl, add milk and stir.
Add meat, onion, egg, salt, and pepper to the Panko mixture. Mix with your hands very well.
Divide the meat into 4 to 6 pieces and roll into oval balls. Push down to flat steaks and make an indentation in the middle.
Heat oil in a frying pan at medium high temperature, place the patties in the hot oil, and fry for 4-6 minutes on one side. Flip over and fry for 3-5 minutes covered until cooked through.
Mix Ponzu sauce ingredients in a small bowl and set aside.
Remove the steak from the pan and top grated Daikon radish and green onion. Drizzle Ponzu sauce over the steak.