For the Miso Marinade: Toast the peppercorns in a small pan over low heat until fragrant. Crush with a mortar and pestle.
Melt coconut oil in a saucepan over low medium heat, add onions and garlic. Sauté until translucent. Add pepper, sauté over low heat until fragrant, add curry powder and fry until fragrant about 1 min. Add remaining ingredients and cook until flavors are combined (2-3 minutes). Cool.
Coat lamb with the marinade and refrigerate for at least 12 hours.
For the Curry Powder: Combine all ingredients. Set aside.
For the Lamb: Preheat the oven to 250°F.
Rinse lamb, dry with paper towels and make incisions throughout the lamb leg. Fill incisions with curry paste and coat the leg with the remainder. (If you have the time prepare and season the lamb the night before.)
Place the leg on a rack in a roasting pan, cover pan with parchment paper and foil, and roast until meat falls off bone (8 to 8 1/2 hours).
Remove from the oven and allow to rest for 30 minutes. Turn your oven up to 400°F.
Unwrap the leg and roast until a crust forms. Remove and season with lemon juice.
Serve with warm roti, cucumber salad and rice.