Place the chopped apples in a large mixing bowl and add the lemon juice. Stir to coat the apples. Add the chopped bacon, broccoli florets, grapes, carrots, scallions and sunflower seeds and stir until well combined. In a separate dish, combine the mayonnaise, sugar and apple cider vinegar and stir until combined. Add the mayo mixture to the other ingredients and stir until well coated. Store in the refrigerator and serve chilled or at room temperature.