Heat up a large cast iron skillet, once hot spray skillet with cooking spray, then pour olive oil into pan.
Add one layer of potatoes to pan, then garlic and salt and pepper. Sautee potatoes and garlic until potatoes are softened, about 10 minutes, stirring occasionally. Chop asparagus while potatoes are cooking, if it's not pre-chopped.
Once potatoes are softened, add in remaining vegetables. Cook for 5 minutes, or until asparagus is slightly softer and brightly colored. Stir occasionally.
Scramble eggs with milk while vegetables are cooking. Add egg mixture to vegetables. Quickly stir asparagus to evenly distribute it. Cover with lid to evenly cook eggs, about 20 minutes.
When eggs are just a bit runny, top with cheese. Cover and cook until tortilla is firm to the touch. (you can also gently shake the pan to see if anything is runny). About 5-10 minutes.
I used asparagus, shredded zucchini, and ham leftover from Easter dinner. You can use any vegetables you have on hand.