Pickled Pepper and Onion Relish

In a small saucepan, combine vinegar, water, sugar, salt, mustard seeds, and peppercorns. Bring to a simmer until sugar dissolves.
In a jar or bowl, layer the sliced peppers and onions.
Pour the hot vinegar mixture over the vegetables, ensuring they are fully covered.
Let the relish cool to room temperature, then refrigerate for at least 2 hours before serving.
Enjoy on sandwiches, burgers, or as a tasty side!