Add fire roasted peppers, Thai red chilis, sherry vinegar, lemon juice, lemon zest, brown sugar, dried oregano, salt, black pepper, and the sauteed onions and garlic to a blender. Blend until nearly smooth.
2 large fire roasted peppers, 6-7 Thai red chilis, ¼ cup sherry vinegar, 3 tablespoons lemon juice, Zest of one lemon, 2 teaspoons brown sugar, 4 teaspoons dried oregano, 1½ teaspoons salt, 1 teaspoon cracked black pepper