Preheat Broiler and line a large baking sheet with foil (or spray with cooking spray.)
In the bowl of a food processor, combine all the ingredients for the marinade, through the salt and pepper, and process until smooth and well combined. Pour over shrimp in a medium bowl, cover, and refrigerate for at least 10 minutes, but no longer than 30.
Meanwhile, whisk together all the ingredients for the southwest cream sauce.
Remove shrimp from marinade and spread onto the baking sheet in a single layer and cook 2-4 minutes, until opaque and cooked through.
To assemble: heat tortillas and top with shredded lettuce, shrimp, chopped tomato and southwest cream sauce. Serve with lime wedges, if desired.