Place fish fillet on a dish. Lightly sprinkle with salt and pepper.
Arrange garlic slices, julienned ginger, and red chili slices on top of the fish. Arrange sour mustard strips and onions around the fish decoratively.
Fill a large wok or pan with about 2 inches of water. Place a metal rack or stand in the wok or pan. Cover with a lid and bring water to a boil.
When the water comes to a boil, transfer dish with fish onto metal rack. Cover, reduce heat to medium, and allow fish to steam for 10 minutes. Fish is done when flesh flakes easily.
While fish is steaming, prepare the dressing. Combine minced garlic and vegetable oil in a small microwavable bowl. Microwave on high for 1½ minutes. Remove, add soy sauce, and stir to combine. Set aside.
When fish is done steaming, remove from wok or pan. Drain some of the juices if there is too much in the dish.
Pour dressing over fish. Garnish with green onions and serve immediately.