A quick to cook version using a pressure cooker (although traditional Guvec is cooked in an earthenware pot) is to fry your onions and cubed lamb in some oil, add either chopped and skinned fresh tomatoes of tinned ones, season with salt and pepper, add some tomato or pepper puree and just enough water to sustain 20 mins cooking at pressure to 'do' the meat.
Meanwhile cut up courgettes and aubergines(preferably the long rather than fat ones) into cubes. i.e. cut the courgette in half down the length then cut the halves again, then chop into inch lengths. Cut up some peppers, red and green, you can add green beans if liked - (but check that these cook fairly quickly otherwise they will need adding to the meat) then put the chopped veggies into a bowl and add olive oil, crushed garlic, sweet red pepper and flakes of chilli pepper, ground black pepper a small amount of dried thyme and if you like a small pinch of cumin, stir all these around so the spices and oil coat the veggies.
Then when the meat has cooked and the pressure released, check there is sufficient juices around the meat - if not add a little water - and pile the veggies on the top, without stirring them in, you can add some chunks of peeled tomato at this stage on top of the veggies. Bring back to pressure and cook for 5-7 mins according to your cooker.
Stir carefully together as you serve I find this method helps to keep the vegetables in good shape.
Serve with rice and a salad