Place bacon in a large skillet and cook over medium-high heat, turning occasionally, until evenly browned, about 10 minutes. Drain bacon slices on paper towels; crumble.

Combine bacon, cauliflower, broccoli, sunflower seeds, and onion in a large bowl.

Whisk salad dressing, sugar, and vinegar together in a jug until blended. Pour over cauliflower mixture and toss to coat.

Refrigerate salad and allow to chill before serving.