Preheat oven to 400ºF. Line a 15 by 10-inch (or larger) rimmed baking sheet with parchment paper.
Combine Spice Mix and reserve.
Cut each squash in half through the stem end. (You may need to carefully rock the chef's knife back and forth.) Scoop out and discard seeds. Place squash halves, cut side up, on prepared baking pan and lightly brush flesh with olive oil. Measure ¼ teaspoon Spice Mix and lightly sprinkle onto cut surfaces of squash. Turn squash over so cut sides are on parchment paper lined baking pan and bake in the center of the preheated oven until tender but still holding their shape, 35 to 45 minutes depending on size.
Meanwhile, prepare filling: Heat olive oil in large skillet over medium heat, add onion and poblano pepper and cook, stirring often, until onion is translucent, 6 to 8 minutes; reduce heat if necessary to avoid over browning. Stir in remaining Spice Mix and cook, stirring, 1-2 minutes. Stir in rice, black beans, and chipotle pepper and mix well. Remove from heat and cool slightly. Stir in ½ cup cheese and 2 tablespoons cilantro.
When squash is tender, remove from oven and turn cut side up. Divide filling evenly among baked squash. Sprinkle remaining cheese on filling and return to the oven. Bake until filling is heated and cheese is melted, 10 to 15 minutes.
Meanwhile, stir together Chipotle Sour Cream ingredients and serve as topping for squash.
Makes 6 side dish servings or 3-4 meatless main dish servings.