In a large mixing bowl, combine minced beef or lamb with grated onion, minced garlic, and spices such as ground cumin, ground coriander, sweet paprika, and chili flakes. Add salt, cracked black pepper, chopped parsley, and bicarbonate of soda. Knead the mixture for about 3-4 minutes until sticky and well-combined.

Lay a piece of parchment paper on a flat surface. Spread the meat mixture into a rectangular shape, about 1 inch thick. Score shallow lines across the mixture to create strips for the kebabs.

Preheat your oven to 240°C (475°F). Transfer the parchment paper with the shaped kebabs onto a baking sheet. Brush the kebabs with olive oil and bake for 15-18 minutes until golden brown.

While the kebabs are baking, prepare the sumac onion mixture by tossing thinly sliced red onions with sumac, lemon juice, olive oil, and sea salt. Let the onions marinate for 5-10 minutes.

In a separate bowl, mix Greek yoghurt with minced garlic, a splash of lemon juice, and a pinch of salt. Stir to combine. Adjust salt and lemon juice to taste.

Warm flatbreads or pita in the oven for about 2-3 minutes until soft.

Once the kebabs are done, slice them along the scored lines. Arrange the slices on the warm flatbreads, topping with sumac onions and garlic yoghurt. Optionally garnish with tomatoes and parsley.