Place a colander inside a bowl. Chop tomatoes and place in colander. Salt tomatoes with 2 tsp Kosher salt and toss. Allow to drain for ~30 minutes, allowing juices to drain into the bowl below.
Preheat oven to 350 degrees. Cut sourdough bread into 1in cubes. Toss with 2 tbsp olive oil. Lay on a baking sheet and toast for 15 minutes. (until toasted and firm, but not too browned). Remove and allow to cool.
Slice red onion thinly. Place in a bowl with 1 tbsp red wine vinegar. Mix onions to coat in vinegar. Allow to sit for minimum of 10 minutes.**
Slice cucumber thinly into bite size pieces.
In the bowl under the colander (the one collecting tomato juice), combine the dressing. Add 6 tbsp olive oil, 2 tbsp red wine vinegar, and minced garlic. Generously salt and pepper, to taste.
In a large bowl, combine tomatoes, red onions, cucumber, chopped basil and dressing.
10-15 minutes before serving, toss in sourdough cubes. Toss well to coat with dressing. Allow flavors to sit for those 10-15 minutes, and serve!