Cut cherry tomatoes in half and cut other tomatoes into about 1/2 inch chunks. Place tomatoes into a strainer and place the strainer inside a wide bowl to catch the juices. Sprinkle tomatoes with salt, mix, and let them stand while you prepare the rest of the salad.
Preheat the oven to 350° and lightly grease a large rimmed baking sheet.
Cut ciabatta loaf onto 1-inch cubes and make them as even as you can.
Toss cubed bread with olive oil and salt and spread into a rimmed baking sheet in one even. layer. Spread them so they are not touching each other and if you need to, use two baking sheets.
Bake croutons for about 8 minutes, take the out of the oven and flip them, and then bake another 8-10 minutes. You want to make the croutons until they are golden brown. Take them out and let them cool on a wire rack.
Transfer tomatoes into a mixing bowl and add sliced cucumber, thinly sliced onion, minced basil, and cooled croutons. Give it a gentle mix and prepare the dressing.
Use the bowl with the tomato juices to make the dressing. Add Dijon mustard, red wine vinegar, pressed garlic, minced basil, salt*, and pepper.
Start whisking vigorously until combined and then, slowly drizzling in olive oil. (Drizzling in the oil slowly while whisking will help emulsify the oil and vinegar together.)
Once it's all incorporated, pour over the salad ingredients and mix everything well.
Let the salad sit for about 30 minutes before serving!
*Additional salt in the dressing is optional since the tomatoes will be salted and so as the juices that drain off of them.