Put half the pomegranate seeds into a sieve over a bowl and use your hands to squeeze out as much juice as possible. Reserve the remaining half of the seeds.
If you are using regular radishes halve, quarter or slice them as you like. The thinner they are the faster any leftover salad will pickle. If you are using daikon slice it as finely as you can then cut into thinnish matchsticks.
Add the pomegranate molasses and vinegar or lemon juice to the bowl of pomegranate juice and season generously with salt.
Put the radishes or daikon and the onion into a bowl and mix with the dressing. Leave to macerate for 15 minutes. Add the herbs, scatter with the reserved pomegranate seeds and sprinkle with sumac if using. Serve.