Place a rack in the upper third of oven, and preheat to 400°F. Use a sharp knife to score flesh of eggplant in a crosshatch design. Brush eggplant halves with 1 Tbsp. olive oil, and lightly season with salt. Roast, skin side down, on a rimmed baking sheet until tender, about 23 to 25 minutes.
In a small bowl, combine remaining 1 Tbsp. olive oil, soy sauce, harissa, and maple syrup; stir with a whisk. Remove eggplant from the oven and increase oven temperature to 450°F. Brush soy sauce mixture over flesh of eggplant, letting it seep into the scores. Place eggplant back in the oven, and roast until glaze is golden and bubbling, about 12 to 15 minutes.
Meanwhile, prepare the Harissa-Tahini Sauce by combining tahini, lemon juice, harissa, maple syrup, and garlic in a small bowl. Whisk to combine, and season with salt and pepper. If needed, add 1 to 2 tsp. water to thin out to desired consistency.
Transfer roasted eggplant to a serving platter, and drizzle Harissa-Tahini Sauce overtop. Scatter cashews and fresh herbs over eggplant, and serve immediately.