Chalupa or Tostada? In Texas, one finds them used interchangeably. Technically, a tostada would be toasted or baked until crisp and a chalupa would be fried. In either case, in Texas and northern Mexico, that shape is not that of a flat bottomed boat or canoe as one sees on a lotería card.
But of a flat, round tortilla made crisp. It differs from the crispy taco (a folded, crisped tortilla) as it gets a slather of refried beans before being topped with beef or chicken, lettuce and tomato, and cheese. Here's a photo of a taco and a chalupa side by side.
For some weird reason, Taco Bell decided not to stick with the standard chalupa profile and went with a wackier, thicker something.
But for me, I will stick with the standard.
For me, the chalupa / tostada is the thing to order in order to reduce the total calories count of a Tex-Mex meal when I am dining out, without sacrificing the crunch or the flavor profile.
At home, I tend to reduce calories even further by going vegetarian, either with TVP or vegetarian chili or one of the newer meat substitutes.
I don't fry my tortillas myself, preferring to use one of the products from Monterrey, Mexico, such as the Charras brand. Ditto if I am not making my own beans from scratch, La Costeña is a good default brand name.
There really isn't a complex recipe to provide you with. Take a tostada, spread frijoles refritos on it, add some protein of your choice, add some salsa picante, and then microwave to heat everything up (about 30 seconds). Top with chopped tomato, lettuce, onions, chiles and cheese and serve. Where you can get creative is with the seasoned meat or TVP.