Holey burgers! Fill your (beef, turkey, salmon, etc.) patty ring with toothsome scoops like veggie chili, spinach and toasted pine nuts, potato and chorizo hash, or edamame and sea salt. Then layer on fixins (pancetta, onions, shiitake mushrooms) and the special sauce of your choice (salsa verde, Jamaican jerk, tzatziki) to build one of 140 million possible combos.