Preheat large skillet over medium heat. Add walnuts; cook and stir 2 minutes to toast. Remove from skillet; set aside.
To assemble sandwiches, spread 4 bread slices with bruschetta topper and 4 slices with mayonnaise. On bruschetta slices layer walnuts, turkey, and spinach; top with mayo slices. Lightly brush sandwiches with olive oil.
Place sandwiches in hot skillet; weight with additional skillet (add food cans for more weight). Grill 2 minutes; turn. Replace weight; cook 2 minutes more or until golden and hot. Serves 4.