Roast lamb with lemon zest recipe

Ingredients

• 500 grams kumara, unpeeled, halved lengthwise, thickly sliced
• 12 uniformly sized chat (baby) potatoes, halved
• 3 medium carrots, quartered lengthwise
• 1/2 cup vegetable or rice bran oil
• 2 medium red onions, cut into thick wedges
• 2 heads garlic, halved crosswise
• 2 tablespoons brown sugar
• 2 tablespoons red wine vinegar
• 2 kilograms leg of lamb
• 2 cups frozen peas
• 1 lemon, zest finely grated
• 1/3 cup finely chopped flat-leaf parsley
• 2 tablespoons finely chopped oregano
• gravy, to serve