Grate the onion, then place it in a fine-mesh sieve and press out the juice. Discard the liquid.
Add grated onion, ground lamb (or beef), minced garlic, chopped parsley, yogurt, olive oil, salt, paprika, coriander, cumin, black pepper, Aleppo pepper, allspice, and cayenne (optional) to a food processor. Blend ingredients until they have a paste-like consistency.
Tear two sheets of parchment paper approximately 10" wide. Place ⅔ cup of the meat mixture between the two sheets and flatten with the palm of your hand.
Use a rolling pin to flatten the meat into a very thin, even layer. Redistribute the meat as needed. Starting from the long edge, fold the meat into 1½-inch folds until you have a compact roll. You should have enough mixture to make 4 rolls.
Place rolls on a rimmed baking sheet, then bake in a preheated 475℉ oven for 10 minutes. Remove from the oven, allow to rest for 5 minutes, then carefully unroll. Tear into strips and serve.
Notes
If you want the meat mixture to be even smoother, blend everything except the meat until you have a paste, then add the meat and blend until well combined.
After tearing into strips, pop them under the broiler or fry in a hot pan for a few minutes if you prefer slightly charred, crispy edges.
Roll it thin! The thinner the meat, the better the layered folds mimic traditional rotisserie doner.
Doner kebab can be prepared ahead of time, and the rolls can be refrigerated or frozen until ready to serve.
Store leftovers in the fridge in an airtight container for up to 5 days.