To make the tostadas, preheat the oven to 400 degrees F. As a note, you can also buy tostada shells!
Place the tortillas on a baking sheet (or 2, if needed). Brush or spray them with olive oil. Sprinkle with salt. Bake the tortillas for 5 to 10 minutes, then flip and bake for 5 minutes more. Let cool slightly before using.
While the tostadas are baking, heat a skillet over medium heat. Add the ground beef and cook until browned, breaking it apart into small crumbles. Stir in the ketchup and mustard until combined. Turn off the heat and add in a sprinkle of cheese - just an ounce or two.
Top each tostada with a sprinkle of cheese, then a spoonful of warm ground beef. Top with more shredded cheese. If you'd like, you can pop this back in the oven here for a minute or so to melt the cheese even more, but the beef does melt it. Drizzle with house sauce. Top with tomatoes, lettuce and pickled onions! Add on pickles or any other condiments you love.