Score the avocado all around with a knife and twist apart at the cut. Remove the stone, scoop out the pulp with a spoon and place in a bowl.
Cut the tomato into as small pieces as possible and place in the bowl. Press or chop the garlic and add it to the bowl. Squeeze half a lemon and add the juice to the bowl. Stir well and possibly mash the avocado with a fork.
Add yoghurt and oil and season with pepper, salt and a little sugar. Stir well again.
Tastes good on fresh bread or baguette, but also as a dip.