Place the peeled garlic cloves into the bowl of a food processor. Pulse the cloves until they are finely chopped. Place the chopped garlic into a small bowl. Wash out the food processor bowl and blade for use again.
Heat the oil in a large pan over medium heat. Add the sliced onions to the oil and toss to coat the onions. Cook the onions, stirring occasionally for about 8 minutes. They will be soft and starting to turn golden brown.
Add the chopped garlic to the softened onions and stir them in with the onions. Lower the heat slightly and cook the garlic with the onions for about 3 minutes.
Add in the Urfa chili flakes, adobo, Sichuan pepper and chipotle pepper and stir them into the onions. Cook the mixture for another two minutes.
Pour in the cider vinegar and increase the heat to medium-high. Bring everything to a simmer and cook for about 5 minutes, until the liquid is reduced a bit and the mixture is thickened.
Let the mixture cool a bit and then transfer to the bowl of the food processor. Blend the mixture until it is smooth. Stir in the oregano leaves.
Transfer the mixture to a heat-proof bowl and allow it to cool. It can be stored in the fridge, covered for up to 3 days.
To use: Trim and prepare the brisket or meat you are using, and place it in on a large, foil-lined pan. Spread the rub over the entire surface of the meat, turning it to coat all sides. Rub the rub in well. Cover the meat and allow it to marinate overnight. Prepare the meat according to your recipe.