Grind the cumin seeds to a fine powder either using a mortar and pestle or a blender. If using a mortar and pestle, adding a pinch of coarse salt helps with getting the seeds ground quicker.
Add yogurt, pineapple, cumin powder, salt, mint leaves and salt to a large blender jar and blend until smooth. Taste and add more salt or cumin if required. If the lassi is too thick, add a little water and blend again.
To serve, add ice cubes to glasses and top with the lassi.