In a strong high-powered blender, combine the frozen açaí, banana, strawberries, lime juice, and yogurt/protein powder (if using).
Blend until completely smooth, tamping down or scraping the sides and adding milk as necessary. You may need more or less liquid, depending on what mix-ins you choose, but keep in mind that the more you add, the less thick the smoothie will be.
Transfer the açaí to a serving bowl and add your favorite toppings. Serve immediately.