Slice the banana right before adding it to the yogurt.
Take yogurt in a bowl along with salt and cardamom powder. Whisk it until smooth.
Add sliced bananas and stir them into the yogurt.
Add red chili powder to the center of the bowl, DO NOT mix.
Heat the oil in a small tadka pan. Once hot add cumin seeds and let them sizzle.
Pour this hot tempering on the chili powder.
Immediately mix it into the raita. Let the raita chill for an hour or so in the refrigerator before serving.
Notes
Raita tastes best when served chilled. So always use chilled yogurt from the refrigerator. Or make this plain raita ahead of time and chill for a few hours before serving.
Slice the banana right before making raita otherwise, the banana oxidizes and gets browning.