In a saucepan over medium high heat, bring the jalapeños, onion and garlic to a boil with enough water to cover. Lower the heat, cover the pan, and simmer for 15 minutes. The vegetables should change in color and be fork tender, but not mushy. Drain and discard water.
Transfer the drained jalapeños, onion and garlic to a blender or food processor, combine with the oil, vinegar, salt and cumin.
Process until smooth and creamy, about 1-2 minutes. Taste for salt, or vinegar and adjust if necessary. Transfer to a squeeze bottle, and refrigerate. It will last for about a week and makes 2 to 2 1/2 cups total.
Perfect to use as a dip or squeeze over tacos, burritos, enchiladas, grilled meats, seafood and roasted vegetables.