I've not eaten at a Taco Bell since I was a young teen, but I'm guessing it's like a tostada? Try marinating flank steak in the juice of two freshly-squeezed limes, two tbs olive oil, two tbs chili powder, 1-4 cloves of crushed or minced garlic, and some pepper. Marinate in the fridge for 2-6 hours or more. Grill the steak on the barbecue or under the broiler till it's done the way you like (preferably only medium rare, at the most cooked). Add any salt you may desire.
Meanwhile, deep fry a large (burrito-sized) flour tortilla. This is annoying and messy and takes a lot of oil, and so you may wish to skip it (though deep-fried tortillas are admittedly yummy). Cut the desired amount of lettuce off of a head of iceburg lettuce and cut lettuce into thin strips. Shred the desired amount of monterrey jack cheese. Cook the desired amount of white rice (add a couple tbs of salsa to it while it cooks, if you want "Mexican" style rice). Assemble tostada. Eat. Dunno if it's at all like what you're thinking of, but it should be yummy, and MUCH healthier than anything you'll get at Taco Bell.