Stir together the pesto and ricotta in a medium bowl. Add salt and pepper to taste, if needed. (You might not need any!) Stir in the egg.
Lay out all 12 lasagna noodles on a clean working surface (like a cutting board). Blot them dry with paper towels so the cheese filling doesn’t get watery. Spread the ricotta mixture onto each of the noodles, leaving a ½-inch margin at one end. Sprinkle the Parmesan cheese over the ricotta filling, then roll up your lasagna, rolling towards the end with the ½-inch margin.
Spread ½ cup of marinara sauce in the bottom of a small freezer-safe baking dish that’s been sprayed with oil or cooking spray. Transfer the roll-ups to the dish, then pour the remaining sauce on top. Sprinkle with the mozzarella cheese.
To freeze:
Cool the casserole completely. Place a layer of plastic wrap over the top, then securely cover the dish with foil (or the lid of the baking dish, if it has one). Transfer the baking dish to the freezer.
To reheat:
Thaw the casserole for 24-48 hours in refrigerator, or remove the foil and plastic wrap and thaw in the microwave. Once the casserole has thawed, cover it with foil and bake it at 350ºF for 30-45 minutes (until it’s warm, but not hot, in the center), then remove the foil and bake until heated through and just beginning to brown on top, about 15 minutes more.
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