Split the cucumbers lengthwise, scoop out the seeds and discard.
Grate the cucumbers coarsely.
Dump the grated cucumbers into a bowl and stir in the yogurt.
Mince the garlic. Stir into the cucumber-yogurt mixture.
Drizzle in the lime or lemon juice. Add the dill. Mix.
Taste the sauce. If you want it more tangy, add more lime or lemon juice. If you prefer a bit of saltiness, sprinkle in a little salt and stir. Adjust to your heart's delight. You're the one who's going to eat it so had better like the way it tastes.
Arrange your fried fish on a platter. Serve the sauce on the side.