Bread: Preheat oven to 350°F (176°C). Combine cubed bread and ¼ cup olive oil in a large bowl, using your hands to work the oil evenly around the cubes. Transfer to a baking sheet and bake for 20 to 30 minutes, or until crisp to the touch (but not browned).
Drain Tomatoes: Cut tomatoes into bite-sized pieces. Set a colander over a bowl and place tomatoes in the colander. Sprinkle with salt and stir to combine, then let tomatoes sit and drain until bread is finished. Reserve the juices that drip out.
Salad: In a large bowl, combine bread, drained tomatoes, bell peppers, cucumber, onion, and basil.
Dressing: Whisk together the juice from the drained tomatoes and all other Dressing ingredients. Drizzle over the panzanella and toss to coat.
Store in an airtight container in the fridge for up to 5 days. The bread is meant to be a little moist in the recipe, meaning the overall flavors and textures shouldn't be impacted if you make it a day or two in advance!