Arrange peppers on a cookie sheet covered in foil. Drizzle with olive oil.
Roast in oven for 30 minutes, until blackened.
Remove stems, skin, and seeds from the serranos. (Leave seeds for extra heat.)
Blend serranos, onions, garlic, vinegar, water, salt, lime juice and zest in a mini processor until smooth. Recipe makes approximately 1/2 cup of salsa.
Keep chilled in the refrigerator until ready to serve, up to one week.
Notes
**The oil from the peppers can burn your skin and eyes, use caution and wash your hands after handling peppers.