To begin, lay your pepper lengthwise on your cutting board.
With a knife, cut off the pepper's top stem. You don't need to trim the tip because the pepper will hold better in your hand when you cut the rings.
Put the cut stem aside. Carefully cut around the inner wall of the pepper to separate the seeds from the flesh. Take out the core and discard.
Wash the pepper under running water and get rid of the remaining seeds inside. Remove any white parts to which the membrane was attached.
Lay the hollowed out pepper on its side, holding it gently to avoid cracking. Using a sharp knife, cut the pepper into rings of your desired width.
Notes
Pepper rings are great for a regular sandwich, or as a garnish for open-faced sandwiches. Depending on the size of the sandwich, cut the rings in half or quarter them.
One other great example is to pan-fry an egg inside of a pepper ring. It is a great way to offer peppers to children, particularly if you use peppers in a variety of colors. This will be an exceptionally attractive dish!
Do you have any freshly cut pepper rings left? Place them in an airtight container or a zip-top bag in the fridge, as they tend to dry out on the surface. They will last about 3–4 days.