To begin, prepare a smoker with apple or apricot wood chips and bring smoker to 225 degrees, following the instruction manual.
Rub the lamb loin generously with olive oil and Mediterranean spice rub. Tightly wrap the lamb loin in plastic wrap and allow it to come to room temperature (25-30 minutes). Remove the lamb from plastic wrap and place in the smoker. Smoke until the internal temperature of the loin is 125 degrees (20-30 minutes).
While the loin is smoking, prepare quinoa, fennel and mushrooms. Start by bringing one cup of water, spices and herbs to a boil. Add quinoa to the broth and simmer until cooked through (18-20 minutes). Strain the quinoa, transfer to a non-reactive bowl and season with lemon juice, olive oil, salt and pepper to taste. Next, place a grill pan over medium-high heat. In a non-reactive bowl, toss fennel and mushrooms in olive oil; season with salt and pepper. Grill fennel and mushrooms on both sides for approximately one minute or until just cooked through; remove from heat and reserve.
Remove the loin from the smoker. Over high heat, bring a cast-iron pan filmed with grape seed oil to nearly smoking and sear lamb on one side. Allow lamb to rest for a minimum of ten minutes; slice and reserve.
To serve, mound one to two tablespoons of quinoa onto a warm plate. Lay slices of fennel and Royal Trumpet mushrooms over quinoa. Place sliced lamb loin, folded over on top of quinoa and garnish with marjoram and smoked Maldon sea salt.