For salsa, brush each cob with oil and grill directly on BBQ grill for 15 minutes or until tender, turning frequently to get all sides evenly and lightly charred. Allow to cool, then cut off kernels and place into a bowl. Combine remaining ingredient together, set aside.
In salted water, microwave or boil sweet potatoes until soft, drain and mash. Add 1/2 tsp oregano and 1/2 tsp cumin, mixing until combined. Set aside.
In a skillet combine cook onion in oil until tender. Stir in beans, lime juice and spices cooking until heated throughout. Remove from heat.
Onto four of the tortillas, spread some of the mashed sweet potatoes, spinach, some of the bean mixture, and 2-3 Tbsp of the cheese. Top with the remaining tortilla and fry/grill for about 3 minutes per side, flipping carefully.
Cut each into quarters and serve with salsa and sour cream if desired.