Yes, you can assemble them ahead of time and store them in the refrigerator for a few hours before baking. Cover them tightly with plastic wrap or aluminum foil to prevent them from drying out. You can also freeze the breasts before baking them. Wrap each stuffed chicken breast in plastic wrap and aluminum foil before placing them in a freezer-safe bag or airtight container. Thaw them in the refrigerator overnight before baking according to the recipe instructions for the best results.