For halloumi burgers, first cut the avocado lengthwise, remove the pit, scoop out the flesh with a spoon and place in a small bowl. Mash until creamy with 2 tablespoons olive oil, the juice and zest of half the lemon and a pinch of salt.
Cut the ciabatta crosswise and spread both halves with the avocado cream.
Slice the halloumi and fry in a little olive oil in a non-stick pan until crispy.
Spread the cheese on the ciabatta halves, top with tomato slices and fold together.
Serve the halloumi burger while still warm.