Chop the tomatoes and sprinkle them with salt.
Place the onion in a bowl, cover with cold water.
Drizzle the bread with olive oil and season with S&P. Grill on both sides until lightly charred. Chop into large cubes.
Drain the onions.
Make the dressing by combining the vinegar, garlic, mustard, sugar, oil and S&P to a bowl and whisking very well.
Add the bread, tomatoes, onion, cucumbers, red pepper, arugula, olives, pepperoncini peppers, capers to a large salad bowl.
Pour the dressing over and toss well.
Add the basil and toss again.