Preheat the oven to 230 °C.
Boil the lentils in plenty of lightly salted water until soft but retaining a bite, 20-25 minutes. Drain, mix with 1 Tbsp olive oil and set aside to cool.
Mix the aubergine with 5 Tbsp olive oil and some salt and pepper. Spread on a baking sheet and bake until browned on the outside and soft in the middle, 30-35 minutes. Set aside to drain on kitchen towels.
Turn the oven down to 200 °C and roast the walnuts until lightly toasted, c. 8 minutes. Chop roughly.
Make the salad dressing by mixing the crushed garlic clove with 2 Tbsp lemon juice, sumac (if using) and extra virgin olive oil. Season.
Make the yoghurt dressing by mixing yoghurt, tahini and 1 Tbsp lemon juice. Season.
When the lentils are no longer hot, mix with the aubergines, tomatoes, red onion, herbs, walnuts and the salad dressing (but not the yoghurt dressing).
When everyone is seated and ready for dinner, fry the halloumi slices in a little olive oil on medium/high heat until golden and crispy on the outside.
Serve the salad immediately with halloumi and yoghurt dressing on the side.
