Pat the tuna steak dry and coat it with sesame seeds so both sides are covered. Sprinkle with black pepper. Heat the olive oil in a skillet until it's almost smoking and sear the tuna for one and a half minutes per side. It should remain red inside; overcooked tuna becomes dry and grainy.
Remove the fish from the pan and let it rest on a cutting board. Heat the sesame oil in the same pan and cook the finely minced ginger and garlic for half a minute.
Add the halved pak choi and edamame beans and stir-fry for three minutes until the stems are tender-crisp and the leaves have just wilted. Drizzle with tamari. Slice the tuna into thick pieces and lay them on the vegetables. Tuna is pure protein, and edamame adds plant-based protein and fiber.