I used to make a similar thing in a toaster oven with two flour tortillas, leftover carne asada and Monterrey Jack cheese in a double stack. The trick was to go light on the salsa, just a very light covering on each. The bottom one was covered with a layer of carne asada after the salsa was spread, then a light sprinkling of cheese to cover, the top tortilla was placed over the bottom one w/ just salsa, given a good shot of cheese, and the foil sheet they were prepared on was slid on to the top rack of the the toaster oven, preheated to about 450 F. Toaster oven temps vary a lot, it's easier to keep an eye on the things cooking than to recommend specific minutes, and allowed to cook until the cheese on top was melted and barely starting to bubble. That was breakfast in my 20's. I like salsa verde for this one, but it's up to you.
You can make a microwave version in under a minute and a half with finished corn tostada shells on a paper plate. With the microwave, you cook until the cheese is just melted. If it bubbles, you're going to get cheese that resembles and tastes like melted plastic when it's cool enough to eat.
It's funny reading Chris's report, but 8 minutes was normally what the double stack finished at in that old toaster oven. I didn't do the pre-bake, but I didn't use as much sauce either, probably a quarter of the amount Chris used on that single tortilla on the entire stack. If you're fan of thin crust pizza's and can't get the crust down, this a dead easy way to go.