I bought a lot of these corn tostadas lately and experimented until I got a recipe for tostada sandwiches just right. The tostadas are also great to heat, break up, and eat just with salsa. I got the corn tostadas in the international section of the grocery, where they are more authentic and tastier than the bland American mass market brands. The brand I bought was "Charras."

Anyway, brown the hamburger in a skillet, breaking it up with a spatula. Drain the grease, then mix in the taco seasoning and water, simmer for 10 min or so until the water is cooked in, then throw the hamburger on a big plate and dump the cheese over the hamburger and microwave for about 3 minutes, or until the cheese is fully melted. I used a store brand of mixed mexican cheeses and it was quite tasty.

While the hamburger and cheese is in the microwave, get out your stack of delicious, crunchy yellow corn tostadas. Turn on your oven (I used a toaster oven) to 350 degrees and put the tostadas in there. If you stack them up, after a few minutes flip the stack over so they cook evenly. You just want to crisp them up and get em nice and hot, don't get them brown or that ruins the flavor.

While the tostadas are cooking (doesn't take long, maybe only 5 min or so, dont let em burn), get out plates and the salsa. Get the hamburger/cheese out and grab the tostadas out of the oven. Spread some hamburger/melted cheese and some salsa on a tortilla/tostada, and then put another tostada on top of it, pick it up and eat it like a sandwich (dipping in ketchup if you are a true chef ). Sounds weird, but trust me, they are awesome