Cut radishes and cucumbers into small bite-size pieces. Toss in a bowl with vinegar.
Add salt, basil, and parsley to taste.
In a small saucepan, stir together vinegar, water, salt, and sweetener. Cook over medium-high heat until simmering.
Thinly slice the red onion and place in a Mason jar.
Pour the hot vinegar mixture over the onions, screw on the lid, and shake to coat the onions evenly with the mixture. Let the onions marinate for at least 30 minutes.
Place radish and cucumber mixture on a plate and top with pickled red onions.