Bring about 4cm of water to boil in a pot fitted with a steamer basket.
In a large bowl, stir together the chilli, garlic, ginger and black bean sauce. Stir in dark and light soy sauces, vegetable oil, sugar and white pepper. In a small cup, mix together the cornflour and water. Stir into the sauce. Cut fish fillets into thin strips, add to bowl and coat well.
When water in steamer has reached a boil, carefully place the tofu cubes in a single layer in the basket and steam, covered, for 2 minutes. Place the fish strips on top of the tofu; cover and steam for another 3 minutes.
Remove and garnish with chopped spring onion. Serve with steamed white rice and stir-fried or steamed Asian vegetables.