To cook lentils, add them to a saucepan with plenty of water and one bay leaf (don't worry if you don't have any, but if you do that's awesome).
Bring to a low boil and cook for approximately 20 minutes, or until cooked but still with some resistance and holding their shape (you'll have to taste a few to check). I start checking from 15 minutes, and if they're still too firm or chalky, give them another 4-5 minutes at a time before checking again.
Once cooked, drain in a sieve and run briefly under cold water. Leave for 5-10 minutes to drain well and continue cooling.
Discard the bay leaf.
Combine lentils, 1 teaspoon olive oil, red onion, mint leaves and cranberries in a mixing bowl. Add a good grind of salt and pepper to season.
For the eggplant:
While the lentils are cooking, put the eggplant in the oven to roast. I like it cut into long wedges (cut in half lengthways, then quarters, then cut each quarter in half again). You can cut it however you choose though. Brush with olive oil and season well.
After 10-15 minutes, turn the eggplant pieces and brush with a little more oil. Roast for another 10-15 minutes or until soft, and darkly golden brown in places.
For the dressing:
Mix all dressing ingredients in a small dish or glass jar. Taste and adjust seasoning as necessary.
To serve:
Serve lentil salad and roasted eggplant with dressing on the side to pour as you like it.