Slice cucumbers thinly
Slice onions thinly
Place cucumbers and onions in a large bowl
Sprinkle with salt
Toss to coat evenly
Let stand for 1 to 2 hours
Rinse well and drain
Combine vinegar, sugar, mustard seeds, celery seeds, turmeric, and pepper in a pot
Bring the mixture to a boil
Add the drained cucumbers and onions
Simmer briefly until heated through
Pack the pickles into clean jars
Pour the hot brine over the vegetables
Seal the jars
Cool to room temperature
Refrigerate before serving
Store in the refrigerator