If using chicken, cut breasts horizontally into two cutlets and halve each cutlet across; or pound thighs then cut into thirds.
If using pork, cut tenderloin in a bias and lightly pound pieces.
If using beef petite filet or flat-iron steak, thinly slice meat.
If using salmon, cut into slices 1-inch thick.
Combine sake or stock, Mirin, soy, ginger and garlic. Start cooking rice.
Bring a few inches of water in a skillet to a boil. Add salt then broccolini and simmer at a low boil for 4-5 minutes. Cold shock and drain; pat dry.
Heat a large, cast-iron skillet or stainless steel pan over high heat with 2 tablespoons oil. Add protein of choice and brown on both sides for 4 minutes per side; remove to plate. Add leeks and stir-fry 2 minutes. Add broccolini and heat though; add sauce and swirl to reduce sauce for 2-3 minutes more.
Slice protein or arrange on a serving platter, top with teriyaki sauce and leeks, and serve with rice.