Mix the mince, onion, scallions and seasoning well together. With wet hands shape into 4 burgers. Flatten each one down with the palm of your hand until you have a nice even shape. This way they will cook more quickly and evenly. Keep in the fridge until ready to cook. Grill, barbecue or cook on a black ridge pan, until fully cooked, 4-5 minutes on each side. Meanwhile mix all the salsa ingredients together. Then place a spoonful of salsa on top of each burger and top with a slice of cheese. Grill, or cover the barbecue or pan and continue to cook for another minute until the cheese has melted.