Tear or slice the sourdough into rustic chunks and place them in a bowl. Cover the bread pieces with cold water and allow them to soak until they become soft and pliable, about 5 minutes. Once softened, squeeze out as much excess water as possible, gently separating and fluffing the pieces with your fingers. Set the prepared sourdough aside until ready to use.
Tear or cut the sourdough into rough pieces and scatter them across a roasting tray. Keep the garlic cloves unpeeled, lightly crush them with the palm of your hand, and add them to the tray. Drizzle the bread generously with extra virgin olive oil, sprinkle with a pinch of sea salt, and toss everything to ensure the pieces are well coated. Roast in a preheated 220°C (430°F) oven for about 10 minutes, or until the bread turns golden with slightly charred edges. Transfer the toasted pieces to a plate and let them cool.
Remove the core from each tomato and cut the tomatoes into bite-sized chunks, placing them in a large mixing bowl. Peel the cucumber, keeping the seeds intact, and slice it into small pieces. Add it to the bowl. Peel and thinly slice the red onion, then scatter it over the tomatoes and cucumbers along with several torn basil leaves. Season the mixture generously with sea salt and black pepper, then allow it to rest at room temperature for several minutes.
After 5 to 10 minutes, the tomatoes will release their juices, forming a flavorful base at the bottom of the bowl. Pour in a generous amount of extra virgin olive oil and finish with a splash of red wine vinegar or apple cider vinegar for brightness. Add a few more basil leaves, then fold in either the soaked or roasted sourdough pieces—whichever method you prepared. Toss the salad thoroughly, ensuring the bread absorbs the tomato juices and dressing.
Let the salad sit briefly so the sourdough softens slightly while still holding some texture. Serve immediately and enjoy this vibrant mix of juicy vegetables, fragrant basil, and tangy olive oil–soaked sourdough.