In a baking dish, place the fish and add the olive oil, salt, black pepper, cumin, coriander and lemon zest.
Rub the spices into the fish until well coated.
Bake for 15 minutes at 350°F (175°C).
In a frying pan, add the olive oil and onions and cook until soft.
Add the pine nuts and cook until the onions are browned.
Add the tahini, yogurt, salt and water. Mix well.
After 15 minutes, take the fish out of the oven and cover with the tahini sauce. Put back into the oven for a further 15 minutes.
Remove from the oven and serve.