Cook bacon in a large skillet over medium heat until browned and crisp. Remove from pan with a slotted spoon, reserving 2 tablespoons bacon fat in skillet, and drain on paper towels.
Add mussels to skillet over medium-high heat and cook, shaking pan occasionally, 3 to 5 minutes or until mussels open. (Discard any that do not.) Place kale in a large bowl, and transfer mussels to bowl with a slotted spoon.
Add vinegar and remaining ingredients to skillet. Bring to a boil; remove from heat, and pour dressing over kale and mussels. Add bacon, tossing gently.