In a large skillet, melt 2 tablespoons of vegan butter or heat olive oil over medium heat. Add 3 sliced sweet onions, stirring occasionally for 25-30 minutes until they turn a rich golden brown. Near the end of cooking, drizzle in 1 tablespoon of agave syrup and a pinch of salt, allowing the onions to caramelize further.

While the onions are caramelizing, blend 14 ounces of drained extra-firm tofu, 1/4 cup of nutritional yeast, and 2 tablespoons of lemon juice in a food processor. Gradually add 1/2 cup of non-dairy oat milk and blend until smooth and creamy.

In a medium saucepan, melt 2 tablespoons of vegan butter over medium heat. Whisk in 2 tablespoons of flour to form a roux, cooking for about 2-3 minutes until lightly golden. Gradually whisk in 2 cups of non-dairy milk, stirring constantly until the mixture thickens, this will take around 5-7 minutes. Finish by stirring in 1 teaspoon of fresh thyme, a pinch of nutmeg, and salt to taste.

Preheat your oven to 375°F (190°C).

In a 9x13-inch baking dish, start by spreading a generous layer of the béchamel across the bottom. Place down your first layer of lasagna sheets, followed by half of the prepared ricotta, a layer of the caramelized onions, and a handful of vegan mozzarella. Repeat until you have filled the dish, finishing with a final layer of béchamel and a sprinkle of mozzarella on top.

Cover your baking dish with aluminum foil and place it in the preheated oven. Bake for 25-30 minutes or until hot and bubbly. Remove the foil during the last 10 minutes of baking to achieve a golden top.