Prepare the Carne Asada according to the recipe directions—heads up! It needs to marinade at least 4 hours (if you've already made it and are using leftovers for this recipe, you can reheat it briefly on the stove with a bit of broth, then add to the fries with the cheese). Slice across the grain, then dice into bite-sized pieces.
Make the fries: To make the fries, place a rack in the lower third of the oven and preheat to 450°F. Place a large rimmed baking sheet in the oven while it heats.
Slice the potatoes into fries: First, cut into ¼-inch-thick planks, then stack the planks on top of each other and cut into ¼-inch sticks. Transfer the potatoes to a large bowl and cover with very hot tap water by at least 1 inch. Let sit 10 minutes. This removes the excess starch so the fries will crisp.
Drain the potatoes and rinse well, then transfer them to a clean dish towel and dry as completely as possible, changing out the towel if needed. Rinse and wipe out the bowl you soaked the potatoes in, then return the potatoes to the bowl. Drizzle with the oil and sprinkle with the salt, onion powder, and chili powder. Toss to coat, making sure the spices and oil are evenly distributed.
Carefully remove the baking sheet from the oven and spread the potatoes into a single layer on the baking sheet. Roast the fries in the lower third of the oven for 15 to 20 minutes, until turning golden underneath. (This is a good time to grill the steak if you haven't already made it).
Remove the baking sheet from the oven and, with a large, sturdy spatula, carefully loosen the fries from the bottom of the pan. Flip them in large sections as best as you can so that the potatoes rotate and brown evenly on all sides (no need to flip every single one). Carefully arrange the potatoes to return them to a single layer. Place the pan back in the oven and continue baking until the fries are as golden and crisp as you like, about 5 to 10 additional minutes.
Top the fries with cheese, then return to the oven for a minute or two to melt. Top with the asada meat and any other desired toppings. Enjoy immediately.
Notes
Nutritional information varies depending on the amount and types of toppings you add.
Cooking time doesn't include the time needed to make the carne asada.
TO STORE: If you have leftovers, store them in an airtight container in the refrigerator for 2 to 3 days (or 1 day if you've topped them with guacamole).
TO REHEAT: Warm up your fries in a 425ºF oven or in the microwave. Note that leftovers won't be as good as freshly made carne asada fries, but they will be edible.