Preheat oven to 450 F (230 C). Grease a large baking dish with a thin layer of oil.
Rinse fermented black beans with tap water, drain, and transfer to a bowl. Use the back of a spoon to smash the beans. Add garlic, Shaoxing wine, light soy sauce, and sugar. Mix well. Or you can skip this step by using pre-made black bean sauce.
(Optional) Halve zucchini crosswise and quartered lengthwise. Or, trim the tough ends from green beans if using. Transfer into a big bowl. Toss with 1 tablespoon oil and sprinkle with salt and black pepper.
Place the fish fillet onto the baking dish, skin side down. If using whole fillet, tuck the very thin part (belly or tail) underneath to prevent overcooking. See the process picture in the blog post as an example.
Spread the black bean sauce on top to cover the surface as much as possible.
Arrange vegetables around without overlapping or covering the fish.
Bake until the fish is just cooked through and flakes easily when lifting the thick part of the fillet with a fork, 10 to 20 minutes. My 1-inch thick whole sea bass fillet finished cooking in 15 minutes.
If the fish cooks faster than the vegetables, transfer the fish to a serving plate and return the baking dish back to the oven. Bake until the vegetables are cooked through.
Serve immediately as main and vegetables as a side.
The amount of oil depends on whether you will bake vegetables with the fish.