Preheat your oven to 350 degrees F (175 degrees C). This is the first step to ensure your casserole cooks evenly and thoroughly.
Spray a 9x13 inch baking dish with nonstick cooking spray and set it aside. This will prevent the casserole from sticking and ensure easy cleanup later.
In a large skillet, heat olive oil over high heat. Once hot, add the diced yellow onion and cook until it becomes tender, about 3 minutes. You'll notice the onion turning translucent, which indicates it's time to add the next ingredients.
Stir in the asparagus, broccoli florets, fresh spinach, and garlic. Cook for an additional 4 minutes, or until the vegetables are tender and the spinach is wilted. Keep stirring to ensure everything cooks evenly.
Next, stir in the chopped artichoke hearts, fresh basil, and half of the green onions. Season with salt and black pepper to taste. The mixture should be fragrant and colorful, with all the veggies well incorporated.
Pour the vegetable mixture into the prepared baking pan and spread it out evenly. This helps ensure every bite is full of those delicious, sautéed vegetables.
In a medium bowl, combine the eggs and Almond Milk. Whisk well until everything is blended together. Season with salt and black pepper again, if desired.
Pour the egg mixture evenly over the veggies and cheese in the baking dish. Make sure it covers all the vegetables well for a cohesive bake.
Top with the remaining green onions and crumbled feta cheese. This will add a nice salty tang and enhance the flavor profile.
Bake for 30 to 35 minutes, or until the eggs are set and slightly golden around the edges. You can test doneness by inserting a knife into the center; it should come out clean. When ready, remove it from the oven and let it cool for 10 minutes before cutting into squares and serving warm.
