Meanwhile, assemble crostini by first mixing roasted peppers, olive paste and remaining oil together. Divide pepper mixture among 12 toasts and place three on the rims of each of 4 plates. Add cockles to littleneck pan and cover. Cook until cockles open, about 1 minute. Add vinegar and escarole and season with salt and pepper. Stir through then divide escarole, clams and cockles among plates and serve.