Place the cucumber slices in a colander; sprinkle with salt. Toss well. Drain 1 hour. Place cucumber slices on several layers of paper towels; cover with additional paper towels. Let stand 5 minutes, pressing down occasionally. Rinse and pat dry.
Combine vinegar, water, sugar, and pepper in a small saucepan. Bring to a boil. Reduce heat; cook until reduced to 1/3 cup (about 10 minutes). Remove vinegar reduction from heat; cool. Stir in onion. Combine cucumbers and vinegar reduction in a medium bowl; toss well. Sprinkle with peanuts.
Made this tonight with some of the 8 million cucumbers we have coming out of our garden right about now. It was DELICIOUS! My husband really liked it too. I will definitely be making this again and I wouldn't change a thing.