Preheat a griddle pan on a medium-high heat.
In a small bowl combine dried oregano, garlic, honey and olive oil. Mix well and brush (or rub) the oil mixture onto one side of the aubergine slices.
Place the aubergine slices oiled side down onto the griddle pan and turn the heat down to medium. Cook for 3-4 minutes. While the first side is cooking, brush the other side of the aubergine slices with the oil mixture. Turn the slices and cook for a further 3-4 minutes.
Use the remaining oil mixture on the bottom side of the portobello mushrooms.
Remove the aubergines from the pan and set to one side. Now add the mushrooms and cook for 4 minutes each side.
While the mushrooms are cooking make the mayo. Add all the burger mayo ingredients to a small bowl and mix well, set aside in the fridge.
Once the mushrooms are cooked, set to one side with the aubergines.
Turn the heat up to high and add the halloumi slices onto the griddle pan for 1-2 mins each side.
Toast your buns in the toaster or under the grill until golden.
Time to assemble the burgers. Evenly spread the burger mayo on one side of the bun, add a halloumi slice, aubergine slice, followed by the portobello mushroom and another aubergine slice. Top with a few slices of tomato and some mixed salad leaves. Repeat for all 4 burgers.