Preheat the oven to 350ºF.
Bring a medium saucepot of salted water to a boil over high heat.
Add the lentils and cook until tender, about 15 minutes.
Drain and return to the saucepot.
Add the tomato sauce and red pepper flakes.
Simmer for 5 minutes, until the lentils begin to break down.
Remove from the heat and set aside.
Bring a large pot of salted water to a boil over high heat.
Add the lasagna noodles and cook until al dente, 2 to 3 minutes less than the package instructions.
Drain and set aside in a single layer so they do not stick together.
In a food processor, combine the tofu, garlic, nutritional yeast, oat milk, olive oil, lemon juice, and nutmeg.
Process until smooth and the consistency resembles ricotta cheese.
Transfer to a large bowl and add the spinach.
Season with salt and pepper and mix to combine.
To assemble, spread a thin layer of the tomato sauce over the bottom of a 9 x 13-inch baking dish.
Top with 5 lasagna noodles, slightly overlapping them.
Add half of the tofu mixture and top with a layer of noodles.
Add a layer of sauce and repeat, ending with a layer of noodles covered with a layer of sauce.
Cover the baking dish with foil and bake for about 20 minutes, until the lasagna is bubbling.
Remove the foil and bake for an additional 10 minutes.
Remove from the oven and allow to cool for at least 20 minutes before serving.
Garnish with the basil, slice, and serve.