Yes, you can prepare most of the elements in advance to assemble at a late time, assemble the entire veggie lasagna to bake later, or even freeze the unbaked lasagna for another time. The elements: The lasagna sheets, bechamel, and vegetable filling can all be prepared in advance. I recommend making the lasagna within 2-3 days, for the best (freshest) results. Assembled in the fridge: Wrap tightly with cling film and keep in the refrigerator for between 2-3 days – bake when needed. Assembled in the freezer: Line your casserole dish with foil or parchment paper (with an overhang!) before assembling the lasagna. Freeze the lasagna until solid and then remove it from the casserole dish. Wrap entirely in more tin foil or plastic wrap and store for between 4-6 weeks. To reheat from frozen: Remove all the foil/plastic wrap and transfer the lasagna back to the baking dish. Allow it to thaw overnight in the refrigerator and then bake as directed. You may need to add just a few extra minutes as you're baking it from chilled.