We made a sauce for shrimp that we imagined also being lovely on fish. It is from Seasonings, the Hatteras Island Cancer Foundation cookbook.
1/2 c fresh lime juice
1/2 sm onion, coarsely chopped
1/4 c water + more for tomatillos
4 jalapenos, seeded and chopped
4 sprigs cilantro
3 garlic cloves, roasted until soft, skins removed
8 tomatillos, husks removed
pinch of salt
In sm saucepan, sprinkle tomatillos with the pinch of salt and cover with water. Bring to boil and cook just until tomatillos change color (to olivey green), about 5 min. Drain and cool.
Transfer to blender or food processor. Add remaining ingredients and puree until you have desired consistency.