Wear gloves when handling hot peppers. Wash peppers, slash 2 to 4 slits in whole peppers, and peel tough-skinned peppers by blanching or blistering.
Flatten whole peppers after peeling; quarter large peppers if desired.
Combine bottled lemon juice, vinegar, oregano, oil, onions, and optional horseradish and heat to boiling.
Place 1/4 garlic clove if using and 1/4 teaspoon salt in each half-pint or 1/2 teaspoon salt in each pint.
Fill jars with peppers and hot, well-mixed oil/pickling solution, leaving 1/2-inch headspace.
Process half-pints or pints 15 minutes at 0–1,000 ft, 20 minutes at 1,001–6,000 ft, or 25 minutes above 6,000 ft.