Preheat the oven to 425°F. Toss the eggplant cubes with 1 tablespoon olive oil and a pinch of salt on a baking sheet. Roast for 20 to 25 minutes until the edges turn golden and the pieces soften.
Add the lentils, diced onion, minced garlic, harissa paste, vegetable broth, diced tomatoes, cumin, salt, and black pepper to the slow cooker. Stir to combine.
Place the roasted eggplant on top of the lentil mixture. Cover and cook on low for 7 to 8 hours or on high for 4 hours, until the lentils are tender.
Stir in the sliced olives and the remaining tablespoon of olive oil. Taste and adjust salt or harissa if needed.
Ladle into bowls and sprinkle with chopped parsley before serving.