Preheat the oven to 375° F. Lightly spray a 12 cup muffin tin with olive oil and place two wonton wrappers in each cup. Rotate each wonton wrapper slightly to cover the whole cup. Bake the wonton wrappers for 5 minutes.
Whisk the eggs, milk, salt, and pepper in a mixing bowl until bubbles form on top.
Remove the wonton cups from the oven and divide the onion, asparagus, and gruyere cheese between wonton cups. Then pour the egg mixture in. Careful not to overfill the wonton cups, they will puff up a bit while cooking.
Reduce the oven temperature to 350° F and bake the egg bites for 15 minutes or until the center has set. When finished, remove from the oven and let them cool for 5 minutes before carefully removing them from the pan.
Garnish with green onions and toppings of your choice.