Heat your oven to 180°C/Fan 160°C/Gas 4. Grease a large rectangular baking dish with ½ tbsp oil. Finely chop the rosemary leaves. Fill a large pan with 450 ml boiling water. Put over a medium heat.
Swirl the water and slowly pour in the polenta. Whisk for 3-4 mins till thickened. Add the rosemary and plenty of seasoning. Pour the polenta into the greased baking dish. Flatten the surface with the back of a spoon. Set aside to cool and set.
Slice the aubergine into 12 rounds. Lay them on a baking tray lined with baking paper. Brush with ½ tbsp oil. Sprinkle with a little salt. Bake in the oven for 15 mins till the aubergine has softened.
Cut the halloumi into 12 thin slices. The polenta should be set by now. Use a cookie cutter similar in size to the largest aubergine round to cut out 12 polenta circles. Alternatively, use a knife to cut the polenta into squares.
Line a baking tray with foil. Place 6 rounds of polenta on the tray. Top each with an aubergine round, followed by a slice of halloumi. Repeat so you have a double layer of each. Bake for 20 mins till the halloumi is oozing and the polenta edges are crisp.
Zest and juice the lemon. Deseed and finely chop the chilli. Peel and crush the garlic. Chuck them all into a food processor with the basil leaves and half the rocket. Add 1 tbsp oil and a little salt. Blitz to a purée. No food processor? Finely chop everything, then whisk in the lemon juice and oil.
Drizzle the cooked stacks with the herby purée. Serve with the remaining rocket leaves.