"This salad has been a family-favorite for years. Even people who don't typically like salad are surprised by how much they enjoy this dish. This is a real winner at potlucks and other large gatherings, as it makes quite a lot of salad."
Place bacon in a large skillet and cook over medium-high heat, turning occasionally, until evenly browned, about 10 minutes. Drain the bacon slices on paper towels.
Whisk mayonnaise, Parmesan cheese, sugar, and basil together in a large bowl until smooth. Add broccoli, cauliflower, and red onion to mayonnaise mixture; toss to coat. Refrigerate salad until chilled and flavors have blended, 3 hours to overnight.
Crumble bacon. Mix bacon, lettuce, croutons, and water chestnuts into salad.