Drizzle the olive oil over the slices of ciabatta bread. Heat a chargrill pan until smoking and toast the bread for 1-2 minutes on both sides, or until golden-brown all over. Remove from the pan and rub the clove garlic onto one side of each slice of toast.
Mix together the tomato, basil, watercress and remaining oil in a bowl, season with salt and freshly ground black pepper and pile onto the ciabatta toasts. Serve immediately.