On a large skillet, cook the bacon until crispy. Reserve the bacon drippings in a small bowl. Place the cooked bacon on a large plate lined with a paper towel.
Scoop 3 tablespoons of the reserved bacon fat back into the skillet. Mix in the apple cider vinegar, mustard and brown sugar.
In a large bowl, toss together the kale and pumpkin seeds. Crumble the bacon on top. Pour the warm vinaigrette on top. Toss and serve immediately.