Slice the eggplant into 1 cm thick rounds. You can leave the skin on or peel it, depending on your preference. Brush both sides of the eggplant slices with olive oil and sprinkle with sumac and salt and pepper.
Arrange the eggplant slices on a baking sheet and roast in the preheated oven for about 20-25 minutes, or until they are golden brown and tender. Once done, remove from the oven and allow them to cool.
While the eggplant is roasting, cook the lentils according to the package instructions. Once cooked, drain any excess water and set aside.
In a small bowl mix all the dressing ingredients and combine until smooth.
In a large mixing bowl, combine the cooked lentils, arugula and spinach, chopped red onion, parsley, sunflower seeds and cooked egplant. Pour over the dressing and mix well.
Let the salad sit for at least 10-15 minutes to allow the flavors to meld together. You can also refrigerate it for a couple of hours to serve it chilled.