Thread the shrimp onto wooden skewers. Place the skewers on a platter, season with salt and pepper and drizzle them with melted butter. Sprinkle with garlic and coriander and turn to coat both sides.
Preheat the barbecue grill.
Grill the shrimp for about 45 seconds each side, or until the flesh is opaque. Remove from the skewers and chop coarsely. Set aside.
Place 4 tortillas on a work surface. Spread with bean puree, leaving a 1 cm (1/2 in) border. Add the diced tomato, avocado and some red onion, then arrange the grilled shrimp pieces over the top. Sprinkle with the Taco Nacho cheese and cover with another tortilla. Press lightly.
Place on the grill and reduce heat to medium-high. Cook about 3 minutes on each side until the tortillas are lightly browned and the cheese is melted. Cut in half and serve with the garnishes.