45 minutes before roasting, remove the lamb shoulder from the fridge and let it sit out at room temperature. This helps even cooking in the oven.
Preheat the oven to 425 degrees F and move the highest rack in the oven to the third highest position.
In a bowl, combine all of the spice blend ingredients and mix. The consistency should be like an oily herbal paste, but if yours feels dry, feel free to add some more oil!
Return to the lamb and trim any excess pieces of fat, or any large membranes coating the meat.
Lay the meat flat and rub the spice blend mixture all over it on the top, bottom, sides or in any crevices. Use all of the spice blend!
Now that your lamb is spiced up and laid flat, lets truss it up! Get a long piece of cooking twine, then tightly roll up the lamb shoulder. Get the cooking twine and set the middle of the string underneath one side of the rolled up lamb. Tie it crossways, moving down the lamb shoulder and wrapping the string around the lamb after every 2 inches. Once the entire roast is tied crossways, tie it lengthways. Tie the twine on the center top portion of the meat. Make sure it stays tight and taught before you put it in the oven!
Place a wire rack onto a sheet pan. Put the lamb shoulder in the center of the wire rack.
Put the lamb into the oven onto the middle rack (the one you moved to the 3rd highest position earlier!) and roast for 45 minutes.
As the lamb is roasting, prepare the parsley and mint dressing by combining all of the ingredients in a jar or bowl, and mixing until combined. Push all of the ingredients to the bottom of the jar or bowl, then add enough olive oil to fully coat the herbs. Mix it up and taste the dressing. Add more herbs, oil, lime juice, salt or pepper to your liking! I wouldn't add a ton of lime juice because it will over power the mint (the star of the dressing!), but a little more is always welcome. The ratios are up to your preference, but the measurements I've provided are what I like.
After 45 minutes, remove the lamb from the oven. Take the internal temperature and if its 115-122, remove it from the heat and let it rest for 15 minutes. It will continue to cook internally and should have an internal temp of anywhere from 120-130 (medium rare) after the resting time. If your lamb is under 100 degrees, let it bake for another 10 minutes, then check up on it again. If your lamb is 110 degrees, let it roast for 5 minutes and then check up on it again. If you prefer a medium or well done preparation, continue to roast and check on the meat every 5-10 minutes until the desired temperatures are reached.Medium = 130 - 140F Well Done= 140-150 F
After the lamb has rested, slice it into 1-1 1/2 inch thick slices. Plate and top with the dressing. Enjoy immediately!