Bring a large pot of salted water to a boil. Add pasta, cooking until al dente, about 8-10 minutes. Drain and set aside.

In a large skillet, heat olive oil and sauté onion until translucent, about 5 minutes. Stir in garlic and spices; cook for 1 minute. Add tomato paste, soy sauce, balsamic vinegar, tomatoes, mushrooms, and lentils. Simmer uncovered for 20-25 minutes, stirring occasionally, and season to taste.

In a medium saucepan, heat olive oil. Whisk in flour for 2 minutes. Gradually add plant milk, whisking until smooth and thickened, about 5 minutes. Stir in nutritional yeast, nutmeg, and seasoning.

Preheat oven to 180°C (355°F). In a baking dish, layer half the pasta, the ragu, then the remaining pasta. Pour béchamel over everything. Add optional topping if desired. Bake for 30-35 minutes until bubbling and golden.

Allow to rest for 10 minutes before serving for easier slicing.