Adjust the oven rack to the middle position and heat the oven to 425 degrees.

Whisk the oil, garlic, cumin, coriander, oregano, salt, and pepper together in a large bowl to create a seasoned base for the vegetables.

Add the sweet potatoes, poblanos, corn, and onion to the bowl and toss thoroughly until the vegetables are evenly coated with the spice oil.

Spread the vegetables in a single layer across two rimmed baking sheets—crowding a single sheet will cause the vegetables to steam rather than roast. Bake until the sweet potatoes are tender and the vegetables are well-browned and caramelized, 25 to 30 minutes, rotating the sheets halfway through.

Remove the baking sheets from the oven and transfer the vegetables to a serving bowl. Toss with the cilantro while the vegetables are still hot so the herb wilts slightly and releases its aroma.

Warm the tortillas in a dry skillet over medium-high heat until soft and charred in spots, about 30 seconds per side.

Fill each tortilla with the vegetable mixture and top with queso fresco, pickled vegetables, and crema. Serve warm, preferably with fresh lime wedges for squeezing.