Step 1) Fill large saucepan approximately 3/4 full of water. Bring to a boil over high heat and add Brussels sprouts. If sprouts are extra large, cut in half lengthwise. Cook uncovered until crisp tender, about 2 minutes; drain.
Step 2) Heat the oil in a large skillet or wok over high heat. Add the Brussels sprouts and stir fry until their edges just begin to turn golden, about 2 to 3 minutes.
Step 3) Combine mustard, garlic powder, sea salt and black pepper in a small bowl. Sprinkle over the sprouts and mix well. Sprinkle lemon peel over and toss to mix well. Serve immediately.