Wash the banana peppers thoroughly, remove the stems, and slice them into thin rings using a sharp knife.
Remove seeds if you prefer a milder pickle, or leave some seeds intact for additional heat and flavor.
Place garlic cloves, oregano, mustard seeds, and peppercorns into clean glass jars before adding the peppers.
Fill the jars with pepper rings, gently pressing them down while keeping enough space for the pickling liquid.
Heat vinegar, water, salt, and sugar in a saucepan until the mixture becomes fully dissolved and slightly warm.
Pour the brine over the peppers, making sure every ring is covered beneath the surface.
Cool the jars before sealing, then refrigerate overnight before using them as a topping or snack.