Once the mushrooms and onions are cooked, add in 1 cup of the almond milk and 1 cup of the coconut milk with salt and pepper and stir until well combined.
Bring the mixture to a boil. While you’re waiting for it boil, combine 2 Tbsp of tapioca starch & 1 Tbsp each of coconut & almond milk and whisk until smooth
Transfer cooked onions to a paper towel. Once the casserole has cooked, scatter the fried onions on top, lightly pressing them into the casserole. Bake for 5 minutes more