Preheat your oven to 375°F (190°C). Oil a 12x17 sheet pan.
In a large pan over medium heat, sauté the spinach with a drizzle of olive oil until the spinach wilts. Remove from the pan and let it cool.
Prepare the Lentil “Meat” Base:
Heat 2 tablespoons of olive oil in the same pan over medium heat.
Add the onion and celery, cooking until softened, about 5-7 minutes.
Stir in garlic, oregano, and basil, cooking for 1 minute, until fragrant.
Add the cooked lentils and balsamic vinegar, marinara sauce and stir to combine. Season with salt and pepper and simmer on low heat for 5 minutes to allow the flavours to meld.
Bring a large pot of water to boil. Add 2 teaspoons of salt and cook pasta for 4 minutes, until slightly under-cooked, stirring to make sure it won't clump.
Drain the cooked pasta and add to the prepared sauce along with 1 cup of mozzarella cheese.
Mix ricotta cheese with the sautéed spinach and parmesan cheese.
Spread the sauce and pasta layer on a baking sheet. Top with dollops of spinach and cheese mixture. Sprinkle the rest of the mozzarella cheese on top.
Bake for 30 minutes, until bubbling and browned on top.
Video
Notes
Refrigerator: Store leftover sheet pan lasagna in an airtight container in the refrigerator for 3-4 days.
Freezer: Freeze leftovers in an airtight container for up to 3 months. Thaw in the refrigerator before reheating.
To reheat: For maximum crispiness, reheat in a 375ºF oven until the lasagna is warmed through. The microwave will also work, but it won’t be as crispy.