Place cucumber slices in a colander and liberally sprinkle salt over cucumbers; set aside until water starts to release from cucumbers, about 15 minutes. Drain and rinse cucumbers.
Mix cucumbers, onions, and green bell pepper together in a bowl.
Whisk sugar, vinegar, celery seed, and 2 teaspoons salt together in a bowl until dressing is smooth; pour over cucumber mixture and stir until evenly coated.
