Marinade:
1 (16 ounce) container plain yogurt
4 sprigs fresh rosemary, leaves stripped
1/2 bunch fresh parsley, stems removed
1/2 head garlic, peeled and smashed
1 1/2 lemons, zested
1/2 (6 pound) leg of lamb
For roasting:
2 large onions, quartered
1/4 cup olive oil
3 tablespoons kosher salt
3 tablespoons ground black pepper
4 sprigs fresh rosemary, leaves stripped
1/2 bunch fresh parsley, stems removed
1/2 head garlic
1 1/2 lemons, zested