Chop the bacon into small pieces and cook it in a large skillet over medium heat for 5-7 minutes until crispy. Transfer to a plate lined with paper towels to drain.

Blanch the broccoli in salted boiling water for 30 seconds, then transfer to an ice bath to stop cooking. Drain thoroughly.

In a mixing bowl, whisk together mayonnaise, vinegar, finely chopped onion, sugar, and raisins. Let the dressing rest for 30 minutes.

In a large bowl, gently fold the cooled broccoli into the dressing. Cover and refrigerate for at least 1 hour.

Just before serving, mix in the crispy bacon and sunflower seeds. Let sit for 10-15 minutes at room temperature before serving.