Slice the cucumbers into thin rounds, roughly 1/8 inch thick, and place them in a colander. Toss with the kosher salt and let them sit for 10 minutes over the sink or a bowl. The salt pulls out surface moisture so your brine stays sharp and does not get diluted. Rinse them briefly and pat dry.

Drain the roasted red peppers from the jar and lay them out on a few layers of paper towels. Press down gently and blot the top as well. Getting them as dry as possible is the key step here because jarred peppers carry a lot of liquid that will thin out your brine if you skip this. Slice them into strips roughly the size of your cucumber rounds.

In a small bowl, whisk together the apple cider vinegar, water, sugar, dried oregano, garlic powder, black pepper, and red pepper flakes if using. Whisk until the sugar fully dissolves, about 30 seconds. No heating required for this brine.

Combine the dried cucumber slices and roasted red pepper strips in a large bowl or a quart-size jar. Pour the brine over everything and stir or shake gently so all the vegetables are coated. Make sure the cucumbers and peppers are mostly submerged.

Cover the bowl or seal the jar and refrigerate for at least 1 hour before serving. For the best flavor, let it sit for a full day. Stir or shake gently before serving. Taste the brine and add a small pinch of salt or a tiny drizzle of olive oil over the top if you like just before plating.