For the shawarma; begin by heating the olive oil over medium heat. Add the yellow onion and sauté for 3-5 minutes. Add the garlic, cumin, turmeric, coriander, black pepper, allspice, cinnamon, clove, fenugreek, fennel seed, and ras el hanout. Cook the oil mixture for about 3 more minutes until the spices are aromatic. Remove from the heat, transfer to stainless steel bowl and allow to cool.