1. Combine mince, onion, garlic, cumin and egg in a large bowl. Using clean hands, shape mixture into four 2cm-thick patties. Spray a barbecue plate or chargrill with oil. Heat over medium-high heat. Cook patties for 3 to 4 minutes each side or until cooked to your liking.
2. Meanwhile, cut bread crossways into four pieces. Cut each piece in half horizontally. Spray cut sides of bread with oil. Cook for 1 to 2 minutes each side or until browned.
3. Spread 4 bread slices with half the dip. Top with spinach, tomato, patties, cucumber and remaining dip. Sandwich with remaining bread. Serve.