Wash and drain mizuna. The greens do not have to be completely dry. Roughly chop into 1-inch segments and set aside.
Place a wide and shallow pan or a wok over high heat. Add the two tablespoons of oil. Add the crushed garlic and stir around for 5 or so seconds.
Add the greens to the wok or pan and saute for 1 minute, stir around constantly. The mizuna should be softened but still crisp. Add the fish sauce and salt and stir around to distribute evenly. Garnish with a squeeze of lemon and freshly ground pepper. Serve warm.