In a small bowl, mix together the Thai red curry paste, soy sauce, fish sauce, and garlic powder. Set aside. If using, mix together the dipping sauce ingredients in a separate small bowl and set them aside, too.
Finely chop the mushrooms and the onion. In a large sauté pan coated with olive oil, cook the mushrooms and onion over medium to medium-high heat, stirring regularly, until the mushrooms release all their liquid and are nicely browned, about 8-10 minutes. Add the ground beef, and continue to cook until the meat is browned, breaking it up as it cooks. When the meat is about halfway cooked, stir in the curry paste mixture (not the dipping sauce if you mixed that up, too), stirring to evenly coat the meat.
To serve: scoop some of the meat mixture on top of individual lettuce leaves. Top with the julienned vegetables and other recommended toppings, as desired. Roll the lettuce around the filling (sort of like a burrito) and enjoy!