Spread 2 to 3 tablespoons peanut butter over half of each tortilla. Top each with some of the marshmallows, chocolate pieces, and banana slices. Fold tortillas in half, pressing gently to flatten and seal slightly. Brush both sides with a little oil.
Place a 10-inch cast iron skillet over medium-high heat on a camp stove, grill rack, or grate over an open fire. Cook tortillas for 2 to 3 minutes per side or until golden and chocolate is melted, turning once halfway through grilling. If desired, sprinkle with sugar and cinnamon. To serve, cut into wedges. Makes 4 servings.