In a deep saute pan over medium, heat the oil. Add the onions and garlic, then cook, stirring occasionally, until the onions turn golden brown and caramelized, about 15 minutes. If they start to darken too much, add 1 tablespoon of water.
Add the peaches, red pepper flakes, allspice, clove, adobo sauce, brown sugar, vinegar and salt. Cook, stirring occasionally, for 45 minutes or until thick.
Working in batches, transfer the mixture to a blender and puree. Adjust the seasoning with additional sugar, salt or vinegar. Transfer the mixture to a clean jar and refrigerate. Keeps for up to 3 weeks.