Slice cucumbers thinly and place in a colander. Toss with 1 teaspoon salt and let rest for 30 minutes.
Rinse cucumbers gently and pat very dry with paper towels to remove excess moisture and salt.
Whisk together sour cream, 2 tablespoons everything bagel seasoning, vinegar, and black pepper in a bowl.
Combine dried cucumber slices and red onion in a large bowl. Pour dressing over and toss until evenly coated.
Sprinkle remaining 1 tablespoon everything bagel seasoning on top. Serve immediately or chill 30 minutes before serving.