HEAT the oil in a large skillet over medium heat and add the chipotle. Cook, stirring, for 30 seconds, being careful not to let it burn. Add the squash, sweet potato, ½ tsp of salt, cumin, and ¾ cup of water. Turn up the heat to medium-high and cook, stirring often, until the sweet potatoes and squash begin to soften, about 6 minutes.
ADD the onion and poblano and season them with another ¼ tsp of salt. Continue to cook, stirring often, until the vegetables are tender and browned on the edges, 6 to 8 minutes more. Add the lime juice and cook, stirring, until it is fully incorporated, 1 minute. Transfer to a serving platter and top with the chopped cilantro.
SERVE with the warm tortillas, Black Beans with Lime, if using, and a selection of toppings.
NOTES: Use 2 dried chipotles or chipotles in adobo if you like extra heat.
You can substitute peeled and diced kabocha for the delicata squash. Butternut squash also works but it will take a bit longer to cook, so sauté it for a few minutes before adding the sweet potato and water.