Preheat the oven to 400F.
Cut the bread into 1 inch cubes. Spread them on a baking sheet and drizzle with the 3 Tbsp olive oil. Toss with the garlic and season with salt and pepper.
Toast the bread in the oven for about 10 minutes, until golden and crispy.
While the bread is toasting, assemble the dressing: combine all ingredients and whisk or shake well. Set aside.
Combine the tomatoes, cucumber, and red onion in a large bowl.
Chiffonade the basil:
Roll the leaves together into a tight bundle.
Add the basil to the vegetables.
Add the toasted croutons to the vegetables.
Dress with the dressing and toss well.
Let sit 15 minutes before serving.