<human>:  How do I make a vegan lasagna?
<bot>: To make a vegan lasagna, start by preheating the oven to 350°F (177°C). Next, cook any type of vegan pasta in salted boiling water until al dente, according to package instructions. Then, sauté mushrooms and onion in a pan with vegan butter or oil, until softened. In a separate bowl, prepare a vegan white sauce by melting vegan butter in a saucepan and whisking in all-purpose flour, garlic powder, nutritional yeast, and plant-based milk. Simmer until desired consistency is reached, stirring constantly. To assemble the lasagna, layer the cooked pasta with the sautéed veggies, vegan white sauce, and vegan cheese. Bake for 40 minutes and serve warm.