Cook the rice, then let it cool completely.
In a mixer, combine cumin, coconut, red chili, cucumber, coriander, and mint leaves. Pulse until coarsely ground.
Alternatively, peel and grate the cucumber.
Heat oil in a kadai.
Add mustard seeds and wait until they splutter.
Season with salt. Add the cooled rice and mix well.
Squeeze some lemon juice over the rice, stir to combine, then turn off the heat.