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.