Preheat the oven to 400°F. Whisk together eggs, cashew milk, sea salt and black pepper. Set aside.
Add olive oil to a 12-inch cast iron skillet over medium heat. Add all but 2 tablespoons green onions, the asparagus, and the mushrooms and saute until vegetables are slightly tender, about 5 minutes. Add spinach and stir to wilt, about 1 minute. Pour in whisked egg mixture and sprinkle with cheese.
Bake frittata for 15 to 20 minutes, or until eggs are set. Remove from the oven and sprinkle with reserved green onions. Slice into pieces and enjoy!
This nutritional information refers to each serving of the entire recipe and not just the products used as ingredients.