Preheat oven to 425°F. Spread butternut squash on a rimmed baking sheet. Toss with 2 Tbsp. of the oil, 1/2 tsp. salt, cumin, and black pepper. Bake for 15 minutes.
Remove squash from oven. Add poblano pepper to baking sheet, along with a touch more oil or cooking spray. Toss to combine with squash. Place back in the oven and bake for 15 to 20 more minutes, until both the squash and pepper are tender.
While vegetables roast, prepare the Harissa-Lime dressing by combining harissa, lime juice, grated garlic, remaining 1/4 tsp. salt, and 3 Tbsp. olive oil to small bowl. Stir with a whisk.
Remove squash mixture from the oven, and add corn to baking sheet. Toss corn with squash and peppers to allow the residual heat and spices to warm and flavor the corn. Transfer mixture to a serving bowl or platter. Drizzle Harissa-Lime dressing overtop, and garnish with feta, pumpkin seeds, and fresh mint. Toss right before serving.