Cut bok choy heads in half lengthwise. Rinse each half thoroughly and trim off the ‘butt’ end. Slice each half crosswise into thin strips and rinse off any remaining water in a colander. Coat top with 1⁄2 tsp coarse salt, and cover with a plate that fits inside the colander. Weigh down the plate with a can.
Meanwhile peel and cut an apple and carrot into matchstick pieces. Place in a bowl and add 1 1⁄2 tablespoons fresh lemon juice, 1 1⁄2 teaspoons canola oil, and 1⁄2 teaspoon grated fresh ginger. Add bok choy to the bowl with the apple and carrot. Add 1⁄2 tsp coarse salt and grated pepper to taste. Stir and refrigerate for at least 15 minutes before serving.
