In a large skillet over high heat, warm the olive oil. Once the oil is hot and shimmering, add in the lamb and break it up into chunks using a spatula or wooden spoon. Spread out into an even layer and sprinkle the salt all over. Let cook, undisturbed, for 5 minutes, or until deeply browned.
Give the meat and stir and continue to break it up into smaller chunks, letting it continue to brown and cook through, about 2 more minutes. If there is more than one or two tablespoons oil in your pan, tilt the pan and use a spoon to remove some of it (we want the fat for flavor and for the spices to toast in, but we don’t want it to be too greasy).
Once it’s mostly cooked through, reduce the heat to low and stir in the cumin, cinnamon, pepper, and garlic for 30 seconds, stirring constantly. Stir in the tomatoes and herbs (if using), then remove from heat.
In a medium bowl, mix together the yogurt sauce ingredients.
Warm up your tortillas over an open flame or in a pan. Top with arugula (if using), lamb crumbles, yogurt sauce, pickled red onions, and some fresh herbs if you have some left over.