Heat the milk: warm 1 cup unsweetened almond milk in a small saucepan over low-medium heat until hot and steaming, about 1–2 minutes; do not boil.
Steep the tea: add 1 chai tea bag to the hot milk and let it steep until the milk is infused, about 3–5 minutes, then remove the tea bag.
Chill the milk: transfer the tea-infused milk to the refrigerator and chill until cold, or you can let it cool to room temperature and refrigerate briefly.
Blend: combine the chilled tea-infused milk, 1 very ripe frozen banana (in chunks), and 1/4 teaspoon pure vanilla extract in a blender and blend until smooth.
Serve: pour into a glass and sprinkle with a little cinnamon if desired, then enjoy immediately.