Preheat your oven to 400°F and line two baking sheets with parchment paper. This step is crucial as it helps prevent sticking and makes for easy cleanup.
On one of the baking sheets, spread the cubed sweet potatoes evenly. Drizzle them with extra-virgin olive oil, ensuring they are well-coated. Sprinkle with a pinch of sea salt and black pepper to enhance their natural sweetness. Roast the sweet potatoes for about 30 minutes until they are tender and start to caramelize.
On the second baking sheet, arrange the mixed mushrooms and asparagus pieces. Drizzle with a bit of olive oil, and add a sprinkle of salt and pepper before tossing everything to coat. These will join the oven during the last 10 minutes of cooking for a wonderful blend of flavors.
While the vegetables are roasting, take a medium-sized bowl and whisk together the eggs, almond milk, minced garlic, salt, and black pepper until well combined. This mixture will bring everything together, providing that lovely custardy texture.
After the sweet potatoes have roasted for 30 minutes, reduce the oven temperature to 350°F. Lightly spray a 9x13-inch baking dish with nonstick spray to ensure easy serving later on.
Now, take the roasted sweet potatoes and spread them evenly across the bottom of your baking dish. Next, add half of the roasted mixed mushrooms and asparagus on top.
Sprinkle the crumbled feta cheese, chopped scallions, and thawed peas over the layered vegetables. This not only adds flavor but also adds beautiful colors to your dish.
Pour the prepared egg mixture evenly over the layered vegetables and cheese, ensuring everything is well-covered.
Add the remaining roasted mushrooms and asparagus on top for an extra layer of flavor.
Place the baking dish in the oven and bake for about 40 to 45 minutes, or until the eggs are set, and the edges are lightly golden brown. Your kitchen will smell incredible when it's almost done!
Once baked, let the casserole sit for about 10 minutes to set further and make slicing easier. Garnish each slice with microgreens if desired. Don’t forget to season with additional salt and pepper before serving.