Preheat oven to 450 degrees. Bake the croissants, cut side down, for five minutes. Remove from the oven and set aside.
Heat the oil. Add the garlic and saute for a few seconds, then add the vegan sausage. Stir-fry for a couple of minutes until the sausage starts to brown. Add the zucchini and bell peppers and the oregano or thyme. Season with pepper and salt and stir-fry for 2-3 minutes until they soften a little. Turn off the heat.
Place the cashews in a blender with 4 cups of water and process into a very smooth milk. If you are using a nondairy milk, you can add the milk directly to the blender. Add the onion flakes, garlic powder, nutritional yeast, nutmeg, and salt and ground black pepper. Mix.
Preheat the oven to 350 degrees.
Butter or oil a baking dish (I used an oval baking dish that's roughly 12 X 9 inches and 3 inches deep and it was the perfect size for this dish).
Place the croissants in the baking dish. I lay some down and make the others stand. It may be a little crowded but that's okay. Scatter on the vegan cheese, reserving some to sprinkle on the top.
Spread the cooked sausage and veggies evenly over the croissants and cheese.
Now pour in the cheesy cashew milk evenly. Press down on the croissants with a ladle to submerge them so they soak up all that cheesy milk. You can either bake this rightaway, or, for the best results, let it stand at least 15 minutes before baking. I like to slide a baking sheet under the dish to make it easy to take it in and out of the oven.
Bake 45 minutes until the casserole is golden and bubbly.
Let stand 5-10 minutes, then serve!