Remove and discard any yellow, damaged, or tough leaves from 1 pound Asian greens such as bok choy, yao choy, or Chinese mustard greens. Trim off and discard tough stem ends. For tough stalks, remove any thick side stems attached to center stalk; discard center stalk and use stems. Rinse well.
For bok choy: Cut leaves and stalks diagonally or crosswise into 1/4-inch-thick slices; separate leaves from stalks.
For Chinese mustard or yao choy: Trim stalk ends, especially if fibrous (a white, woody center is an indication). If skin on stalks is tough, peel off and discard. Cut greens into 3-inch lengths, separating leaves and thin stems from thicker stems or stalks. If any pieces are thicker than 1/2 inch, cut to that thickness.
Set a 14- to 16-inch wok or 12-inch frying pan over high heat. When hot, add 1 tablespoon vegetable oil and 1 tablespoon chopped garlic; stir until garlic begins to brown, about 15 seconds. Stir in thicker stem or stalk pieces and 3 tablespoons water. Cover and cook until stems are tender-crisp to bite, 2 to 3 minutes. Uncover, add leaves and thin stems, and stir until leaves are barely wilted, 1 to 2 minutes. Add salt to taste and pour into a serving bowl.