Spread ketchup evenly over the tortilla. Grate cheese (if not factory grated) and sprinkle over the ketchup. Microwave for 30 seconds. If you have one of those microwaves that can nuke a city, you might wanna go for about 20. Check occasionally to make sure it isn’t burning. The cheese should still be in it’s little grated strips, just spread out more and bubbling slightly.