How to Make It
In a bowl, whisk the yogurt with the garlic, lemon juice, rosemary, olive oil and 1 tablespoon each of salt and pepper. Rub the mixture all over the lamb and set on a large rimmed baking sheet. Cover with plastic wrap and refrigerate overnight. Let the lamb stand at room temperature for 1 hour before roasting.
Preheat the oven to 375°. Season the lamb lightly with salt and pepper and roast for about 1 hour and 50 minutes, until an instant-read thermometer inserted in the thickest part of the meat registers 140°. Transfer to a carving board and let rest for 30 minutes.
In a food processor, pulse the basil, parsley, garlic and lemon juice with a pinch of salt until minced. With the machine on, gradually add the olive oil until incorporated. Scrape the pesto into a bowl and stir in the hemp seeds. Season with salt and pepper. Carve the lamb and serve with the pesto and lemon wedges.