Slice the kernels off the corn cobs and transfer to a large mixing bowl. Combine with the tomatoes and red onion. Make a dressing of the olive oil mustard and vinegar and season to taste with salt and pepper. Add the dressing to the vegetables and toss; marinate overnight. Right before serving, combine the zucchini with the rest of the ingredients; transfer them to a platter lined with lettuce and garnish with pitted olives.