PREHEAT oven to 450º F. ADJUST over racks for roasting two trays.

SLICE onions and bell pepper into wide strips; CHOP sweet potato. PLACE in a large bowl with black beans.

MIX in the olive oil, cumin, chili powder, garlic powder and kosher salt. STIR until everything is evenly coated.

LINE two baking sheets with parchment paper or silicone baking mats. SPREAD the vegetables evenly onto each sheet.

BAKE vegetables for 20 minutes; ROTATE pans and roast for an additional 10 minutes, until tender and lightly browned on one side.

CUT lime into wedges; SPRITZ vegetables with fresh lime juice to taste, approx. 2 wedges per sheet.

WARM and char tortillas over open gas flame on medium for a few seconds per side, flipping with tongs, until they are slightly blackened and warm.

TOP tortillas with roasted vegetables, pico de gallo and cheese crumbles, if using. TOP with sour cream and chopped cilantro.