Preheat oven to 350°
Heat the oil in a large skillet over medium high heat.
Add the onion and sauté for 3-5 minutes until onion softens.
Add the sweet potatoes and sage
Reduce heat to medium low, cover the pan and cook for 10 minutes until sweet potatoes are tender.
Remove from heat and stir in the asparagus.
Whisk the eggs, milk, salt and pepper together in a small bowl.
Arrange the veggies in the bottom of a 9″ square (or similar size) baking pan.
Pour the egg mixture over the vegetables.
Top with grated cheddar and feta.
Bake for 30-40 minutes until egg is set and the top starts to brown.
Serve hot or at room temperature.