Mix the tomatoes, cucumber, red pepper, onion, garlic, and bread crumbs in a medium glass bowl. Add the vinegar, stock, thyme, and 12 of the basil leaves. Cover the bowl with plastic wrap, and marinate 12 hours in the refrigerator.
Puree the mixture, and season to taste with salt, pepper, and cayenne pepper. If too acidic (and this will depend on the tomatoes you've used), add a little honey.
Serve cold with the remaining basil leaves shredded and scattered over top along with some croutons, if using.