Cook the farfalle pasta according to package directions until tender but still firm. Rinse under cold water, drain thoroughly, and refrigerate for at least 1 hour.
In a medium bowl, whisk together mayonnaise, sugar, vinegar, and salt. Set aside in the fridge to keep cool.
Chop the broccoli, dice the red onion, and cut the grapes in half.
In a large mixing bowl, combine the chilled pasta, broccoli, red onion, and grapes. Pour the dressing over and stir gently to combine.
Cover and chill for at least 2 hours to allow flavors to meld.
Just before serving, stir in the sunflower seeds, chopped pecans, and crumbled bacon.
Notes
Store leftovers in an airtight container in the fridge for up to 3 days. Keep crunchy toppings separate until serving.