Place vegetable oil and garlic in a small microwave safe dish. Microwave on high for 1½ minutes.
Remove from microwave. Add soy sauce and mirin. Stir to combine.
Remove tofu from container. Drain and place tofu in a separate microwave safe dish. Cover with a piece of wax paper. Place the tofu in the microwave.
Cook for 5 minutes at 80% power. Reducing the power level prevents tofu from "bursting" or "exploding" during cooking. Alternatively, you can steam tofu in a steamer for 5 minutes.
Remove tofu from the microwave and drain off excess liquid. Transfer to a serving dish, if preferred.
Spoon dressing over tofu. Garnish with spring onions and optional toppings (if using).