Heat one side of a gas grill to medium or light a charcoal fire and let it burn until the coals are covered with gray and still quite hot.
Combine the mayonnaise, chiles, and lime juice in a small food processor or blender and process until smooth. Add a little water if needed so the mixture runs smoothly through the blades. Transfer the chipotle mayonnaise to a small bowl.
Line a platter with the greens, lime wedges, red onion slices.
Thread the tuna onto skewers. Spray or brush with oil and sprinkle with salt. Place on grill and grill for about 2-3 minutes. Brush with some of the chipotle mayo and flip to the other side. Brush the other side with more mayo and grill for 2-3 minutes more.
Remove the skewers from the grill and transfer to your platter. Serve with warm tortillas.