Tear the 3 thick slices of Italian bread into small 1-inch chunks and place in a medium mixing bowl. Add the red wine vinegar and toss to coat the bread and allow to soak for 10 minutes.
In a small bowl, add the tomato paste and mix in 2 tablespoons of warm water to dilute. Set aside.
Into the bowl of a food processor, add the capers, garlic, parsley and olive oil until you get a coarse chop. Add the soaked bread and tomato paste and mix until all the garlic is finely chopped. Season with salt and pepper, to taste.
Spread the mixture onto the toasted crostini slices and serve.