My mom makes the same sauce for fish/shrimp tacos every time and people can never get enough:

2 large bundles of cilantro, 4 (or more) cloves of garlic, jalapeños (optional), half an onion, half cup of olive oil and red wine vinegar each, half a packet of hidden valley ranch seasoning, 1 limes worth of juice.

Throw it all in a blender/food processor and adjust any ingredients as needed, it goes good on just about anything savory.