COOK RICE: Preheat the oven to 425 degrees F. Combine rice, coconut milk, and 1/4 teaspoon salt In a small pot. Stir. Bring to a boil over high heat and then reduce to low, cover and simmer for about 15-20 minutes or until coconut milk is absorbed. Remove the pot from the heat (keeping it covered) and let it stand undisturbed for 10 minutes. After that, fluff it with a fork and stir in 1 finely sliced green onion. Set aside and keep warm.
PREP: While rice cooks, peel the sweet potato and then cut into 1/2 inch rounds. Cut the rounds in 1/2-inch pieces. Quarter the mushrooms.
ROAST VEGGIES: Whisk together 2 tablespoons soy sauce, 2 teaspoons Sriracha sauce, 1 tablespoon brown sugar, and 1 tablespoon vegetable or canola oil in a small bowl. Line a baking sheet with parchment paper (don't skip this step; the mixture gets sticky!). Place chopped sweet potatoes and mushrooms on the baking pan and then pour the mixture over. Stir to mix the ingredients, and space out the veggies in a single layer. Bake for 10 minutes, flip the veggies with a spatula, and then bake for another 10-15 minutes or until veggies are tender. Remove from the oven and season to taste with salt.
DRESSING: While veggies are roasting, add 2 tablespoons rice wine vinegar, 3 tablespoons canola oil, 1 teaspoon brown sugar, 1/2 teaspoon finely minced ginger, and remaining thinly sliced green onion. Season to taste with salt. If desired add in crushed red pepper flakes. Stir dressing until combined.
ASSEMBLE: Wash and thoroughly (but gently) dry the lettuce. Double up 2 pieces of lettuce or use single pieces of lettuce, depending on how thick your lettuce is. Fill the lettuce cups with a generous spoonful of the rice. Add the veggies on top and then drizzle the dressing on generously. If desired, garnish with crushed cashews and a thinly sliced cucumber. Season with additional salt and pepper if needed. If desired, add a tiny drizzle of sesame oil or lime juice over the wraps. Serve extra rice on the side with any leftover dressing. Serve immediately.