Fill a large pot with lightly salted water and bring to a rolling boil. Stir in shells and return to a boil. Cook pasta uncovered, stirring occasionally, until tender yet firm to the bite, about 6 minutes. Drain. Transfer to a bowl and refrigerate until cool, about 20 minutes.

Combine creamy salad dressing and bacon ranch dressing in a large bowl. Mix in cooled pasta, lettuce, tomato, cucumber, green onions, and bacon bits. Refrigerate until serving.