Add the frozen strawberries, frozen watermelon cubes, and frozen banana slices to a high-speed blender.
Pour in the almond milk and add honey if using. Start blending on low speed, using a tamper to push the fruit toward the blades.
Gradually increase to high speed and blend for 45-60 seconds, stopping to scrape down the sides as needed. Add more almond milk 1 tablespoon at a time only if the blender struggles, keeping the mixture as thick as possible.
Blend until completely smooth and the consistency resembles thick soft-serve ice cream. The mixture should hold its shape when scooped with a spoon.
Pour the smoothie into a chilled bowl, using a spatula to scrape out every bit.
Top with your choice of fresh strawberry slices, watermelon chunks, granola, chia seeds, coconut flakes, or nut butter. Serve immediately with a spoon.
