Peel ginger. Grate half of it and thinly julienne the other half.
Add grated ginger, sake, mirin and soy sauce to a large mixing bowl. Mix until combined. Add pork and mix to coat each piece in the marinade evenly. Cover and let marinate in the fridge for 10-15 minutes.
Heat up olive oil in a large nonstick skillet over high heat. Add marinated pork and cook until it changes color, stir-frying constantly.
Add julienned ginger and cook for another 30 seconds, stir-frying constantly.
Remove from heat immediately and serve with steamed rice. Garnish with chopped scallions and sesame seeds. Enjoy!