In a food processor, pulse all ingredients except toppings until well combined and fairly smooth.

Shape mixture into four equally sized patties. Cover with plastic wrap and refrigerate while the barbecue heats up.

Oil the grid and preheat barbecue to medium-high.

Grill patties with lid closed for 8 to 10 minutes, flipping halfway through.

In the meantime, brush onion rings with a little oil and grill until tender—about 4 minutes each side.

At the end of cooking, heat buns on the grill for 2 minutes or until golden.

Garnish each bun with a patty, mayonnaise, lettuce, cucumber and grilled onions. Serve with your choice of green salad.