Bring vinegar, honey, sea salt, pepper and red pepper to a boil. Pour over onions and allow to sit for at least 30 minutes.
Drain vinegar, reserving 3 tablespoons for dressing. Place onions and tomatoes in a bowl and toss together. Make dressing by combining reserved vinegar, mustard, sea salt, pepper and olive oil in a blender. Process until smooth and then pour over onions and tomatoes. Top with goat cheese and serve at room temperature.
Notes
Storage
This salad is best served the day it is made because tomatoes get mushy when refrigerated.If you would like to store it, it will keep for up to three days in a sealed container in the refrigerator.