Combine the mince, sage, egg, shallot, half the cranberry sauce and breadcrumbs in a large bowl. Season with salt and pepper.
Shape the mixture into four 2cm-thick patties. Heat the olive oil in a large frying pan over medium-high heat. Cook the patties for 7 minutes each side or until browned and cooked through.
Meanwhile, preheat a chargrill on medium-high. Cook the corn for 10 minutes or until lightly charred.
Add vegetable oil to a large frying pan to a depth of 2cm. Heat over medium-high heat. Cook half the sweet potato for 2-3 minutes or until crisp and golden. Transfer to a plate lined with paper towel. Repeat with the remaining sweet potato. Season with salt.
Spread the mayonnaise over bread roll bases. Top with lettuce, tomato, onion and turkey patties. Spread with remaining cranberry sauce. Serve the burgers with the corn and sweet potato crisps.