Preheat the oven to 400°F (204°C).
Pulse onion and garlic in a food processor until finely chopped.
Add beef, tomato paste, yogurt, cumin, paprika, pepper flakes, salt and black pepper and mix well.
Split the mixture into three equal portions.
Place meat on parchment paper and flatten into rectangles.
Roll the meat tightly using parchment paper and place on a sheet pan.
Add tomatoes and peppers to the pan and drizzle with olive oil, salt and pepper.
Bake for 20 minutes until cooked and slightly browned.
Unroll the meat and tear into large doner-style chunks.
Melt butter and mix with tomato paste, hot water and salt until simmering.
Spread sauce on lavash, add doner meat, roasted vegetables and onions.
Roll tightly, slice in half and serve.
