Cook the bacon by chopping it into small pieces and heating a skillet over medium heat. Cook for about 5-7 minutes until crispy, then drain on paper towels.

Prepare the broccoli by bringing salted water to a boil. Blanch the chopped broccoli florets for 30 seconds and plunge them into an ice bath, then drain thoroughly.

Make the dressing by combining mayonnaise, vinegar, chopped onion, sugar, and raisins in a bowl. Whisk together and let sit for 30 minutes.

Combine the cooled broccoli and dressing in a large bowl and toss gently. Cover and refrigerate for at least 1 hour to allow flavors to meld.

Before serving, fold in the crispy bacon and sunflower seeds, and let the salad sit at room temperature for 10-15 minutes to enhance flavors.