To a high-speed blender, add frozen bananas, protein powder, soy milk, instant coffee, cocoa, and vanilla. Pulse until smooth and creamy. (Add a tablespoon of soy milk as needed if the blades of the blender get stuck.)
With a rubber spatula, scrape out the smoothie into a bowl. Sprinkle with your favorite toppings, such as chia seeds (for extra protein), chopped nuts, sliced bananas or berries, mini dairy-free chocolate chips, or granola.