Step 1

With the rack in the middle position, preheat the oven to 400°F (200°C). Line a baking sheet with parchment paper.

Step 2

On the baking sheet, toss the onion wedges with the oil. Season with salt and pepper. Bake for 30 minutes or until the onion is tender and golden.

Step 3

Meanwhile, in a small food processor, purée all of the ingredients until fairly smooth. Season with salt and pepper. Set aside.

Step 4

In a bowl, combine the ground lamb, breadcrumbs, sumac and egg. Season with salt and pepper. Using your hands, form the mixture into 4 patties.

Step 5

In a large skillet over medium heat, cook the patties in the oil for 4 to 5 minutes on each side.

Step 6

Cover the bun bottoms with the sour cream. Top with the patties, roast onions, arugula and pesto. Close with the bun tops.