Roast the poblanos. Char the peppers over a gas burner or under a broiler until the skin is blackened all over. Remove them from the heat, place in a bowl and cover with a towel or plastic wrap for 10 minutes. Uncover and use your hands to peel and remove the loose skin. Slice off the stem, and remove the seeds, and slice it into strips.

Assemble tortillas with sprinkles of cheese, sweet potatoes, poblano slices, bell pepper, black beans, scallions, and serrano, if using. Fold each tortilla in half and cook in a hot skillet for about 2 minutes per side. Serve with guacamole, salsa, lime wedges, serranos, and cilantro.