Step 1Cut a thin lengthwise slit on each side of each pepper to allow the brine to penetrate.
Step 2In a medium saucepan, simmer the vinegar with 2 cups of water, the garlic, salt, sugar, oregano, peppercorns, onion and dried chile, if desired, until fragrant, 3 to 4 minutes.
Step 3Blanch the peppers in a large pot of boiling water until they begin to soften and the color just begins to fade, 2 to 3 minutes. Drain the peppers and pat dry with a kitchen towel; do not rinse them.
Step 4Place the peppers, still warm, in a large nonreactive container with a cover and pour the vinegar solution over them. Seal tightly and refrigerate at least 8 hours.