Place the lamb pieces, lemon juice, cumin, oregano, sumac, chilli flakes, sea salt and 1 tablespoon oil into a large bowl or resealable bag along with the bashed garlic cloves. Mix well so that the lamb is thoroughly coated. Leave in the fridge to marinate for a few hours, preferably overnight.
Brush the courgette, aubergine, pepper, lettuce and tomatoes with a little oil. Sprinkle with salt and pepper. Heat a griddle pan (ideally cast iron) over medium high heat and griddle the vegetables in batches until they are nice and soft and charred. This should take a couple of minutes per side, depending on how well your pan conducts the heat. Place the cooked veggies into a bowl and pour over the lemon dressing. Mix well.
Place the lamb cubes onto skewers along with the garlic cloves, if liked, and griddle for a few minutes per side until cooked to your liking.
Served the cooked lamb and vegetables with warm pitta bread and sumac tzatziki.