Preheat the oven to 350°F. Bring a large pot of salted water to a boil and cook the lasagna noodles according to the package directions until just tender. Drain carefully and set them aside.
While the noodles cook, heat the olive oil in a large skillet over medium heat. Add the onion and cook for 4–5 minutes, until softened and translucent. Stir in the garlic and cook for about 30 seconds, just until fragrant.
Add the diced eggplant, salt, and black pepper. Cook for 8–10 minutes, stirring occasionally, until the eggplant becomes tender and soft.
Add the vegan ground meat and Italian seasoning. Break the crumbles apart with a wooden spoon and cook for 3–4 minutes, until heated through and lightly browned.
Pour in the marinara sauce and red pepper flakes, if using. Stir well and let the mixture simmer gently for 3–5 minutes. Taste and adjust the seasoning as needed.
Spread a thin layer of the sauce mixture across the bottom of a 9 × 13-inch baking dish.
Arrange a layer of lasagna noodles over the sauce, slightly overlapping them if necessary.
Spread about one-third of the vegan ricotta over the noodles, followed by one-third of the remaining sauce and a sprinkle of vegan mozzarella.
Repeat the layers with more noodles, ricotta, sauce, and mozzarella until all the ingredients are used, finishing with a layer of sauce and the remaining mozzarella on top.
Cover the baking dish tightly with aluminum foil and bake for 30 minutes.
Remove the foil and continue baking for 10–15 minutes, until the sauce is bubbling and the vegan mozzarella is melted. For a more golden topping, broil for 2–3 minutes, watching closely so the cheese does not burn.
Remove the lasagna from the oven and let it rest for 10–15 minutes before slicing. This resting time helps the layers set and makes the lasagna much easier to serve.
Garnish with fresh basil and serve warm.