Prepare Onion: Grind or finely process two large onions in a food processor. Remove the juice by straining it out and discard or save for marinade.
Mix Spices and Onion: Add 2 teaspoons salt, 1 teaspoon black pepper, 3 teaspoons sumac, and optional 1/2 teaspoon garlic powder to the grated onion. Mix well.
Combine Meat and Onion Mixture: Add 1 kilogram ground beef to the onion-spice mixture. Mix aggressively by hand for 5-6 minutes until the mixture is sticky and well combined.
Rest the Mixture: Set the meat mixture aside for about 1 hour to allow flavors to meld.
Prepare Parsley Condiment: Roughly chop a handful of parsley leaves and mix with some grated onion and sumac to create a fresh condiment.
Prepare Musir Yogurt Sauce: Soak musir (dry shallot) in hot water for about 2 hours until soft. Finely chop and mix with yogurt and a pinch of salt to make the sauce.
Prepare Tomatoes: Cut tomatoes in half if large. Grill them until slightly charred.
Form Kebabs: Wet your hands with warm water. Take about 80-100 grams of meat mixture, shape it onto skewers by pressing firmly and closing the ends tightly.
Grill Kebabs: Preheat grill. Place kebabs and grill tomatoes on the grill. Turn kebabs every 5-10 seconds initially to prevent falling off. Cook until done, controlling flame and heat.
Assemble Burrito: Place grilled kebab, grilled tomatoes, parsley condiment, and musir yogurt sauce on a large burrito tortilla. Wrap tightly and serve.