Preheat the Oven: Set your oven temperature to 400°F and allow it to preheat.
Season and Roast the Eggplant: In a small mixing bowl, combine ⅓ cup of olive oil with the harissa, ground cumin, and 1 teaspoon of salt. Stir until well blended. Toss the eggplant chunks in the mixture, ensuring they are evenly coated. Spread the eggplant onto a large, rimmed baking sheet in a single layer. Roast in the oven, stirring occasionally, until the pieces become golden brown and tender, approximately 20 minutes.
Prepare the Shrimp: While the eggplant roasts, pat the shrimp thoroughly dry using paper towels. In another bowl, toss the shrimp with 1½ tablespoons of olive oil, cumin seeds, lemon zest, ¼ teaspoon salt, and black pepper. Lay the shrimp out evenly on a separate rimmed baking sheet to ensure they cook uniformly.
Increase the Oven Temperature and Roast Everything: Adjust the oven temperature to 425°F. Place the shrimp in the oven alongside the eggplant. Roast both until the shrimp turn pink and are just cooked through, and the eggplant reaches a caramelized, golden finish. This process should take about 7–10 minutes. If the shrimp finish cooking before the eggplant, remove the shrimp and let the eggplant continue roasting until done.
Combine and Serve: Arrange the roasted shrimp and eggplant together on a serving platter or divide them among individual plates. Drizzle the dish with additional olive oil and a squeeze of fresh lemon juice. Finish by garnishing with torn mint leaves for a bright, fresh touch.