Place the cucumber slices in strainer placed over a plate. Season with the 1/4 teaspoon of salt then toss to coat evenly. Place in the refrigerator for 30 minutes.
Place the drained cucumber slices in a serving bowl. Add the vinegar, red onion slices, fresh dill, and crushed red pepper flakes, to taste; toss to coat evenly.
Place in the refrigerator for 30 minutes before serving.
Toss before serving then taste and season with sea salt and freshly cracked pepper, to taste.
Serve and enjoy.