How to Make It
Preheat broiler with rack 6 inches from heat. Line a rimmed baking sheet with parchment paper.
Toss together poblanos, squash, and oil in a large bowl. Arrange poblanos and squash separately on prepared baking sheet. Toss squash with ½ teaspoon ancho chile powder, ¼ teaspoon salt, and ￼ teaspoon pepper. Broil, stirring once halfway through, until poblano skins are charred and squash is tender, 8 to 10 minutes. Let cool 5 minutes, then skin, seed, and slice poblanos.
Stir together sour cream, lemon juice, and remaining ½ teaspoon ancho chile powder, ¼ teaspoon salt, and ⅛￼ teaspoon pepper in a small bowl. Toast tortillas under broiler until golden and warm, about 30 seconds.
Assemble tacos with tortillas, sour cream mixture, squash, poblanos, cheese, cilantro, and pumpkin seeds.