Heat the oven to 180C/fan 160C/gas 4. Grease and line the base and ends of a 500g loaf tin with baking paper (a shallow, wide one gives the best shape for lots of topping).
Soften the onions in 1 tbsp oil over a low heat until golden. Scrape into a bowl and stir in the garlic, then leave to cool for 5 minutes.
Squeeze the sausage meat from their skins into the bowl with the cooled onions, then add the pitta crumbs, parsley, 2 tsp of the oregano, allspice, lemon zest, tomato purée, diced olives and egg. Season well, then mash together with your hands.
Push the mixture into the prepared tin, smooth the surface and bake for 35 minutes until firm. Carefully turn out of the tin onto a baking sheet. Turn the oven up to 200C/fan 180C/gas 6 and tear the remaining stale pitta into pieces, then scatter over the top with the crumbled feta and remaining ½ tsp of oregano.
Drizzle with a splash more oil, then bake again for 10-15 minutes to crisp up the top, and turn the pitta golden brown.
Cut the zested lemons into wedges, and serve with slices of the meatloaf, salad leaves and tomatoes.