Preheat the oven to 350°F. Oil the bottom and sides of a 10-inch cast iron or deep oven safe skillet. Set aside.
Drizzle the skillet with olive oil. Add the beef, onion, garlic, garlic salt, lemon pepper and oregano Cook over medium high for 10 minutes or until no pink remains. Drain excess fat from the pan.
Add the salsa and taco seasoning to the browned meat. Simmer on low for 5 minutes.
To assemble: layer 5 tostadas on the bottom of the skillet overlapping. spread with ½ refried beans, ½ ground beef and sprinkle with 1 cup cheese.
Repeat, 5 tostadas, spread with ½ refried beans, ½ beef and 1 cup cheese.
Top with 5 tostadas leaving 1-inch border around the edge. (This will to allow taco sauce to drip into the skillet while baking).
Pour taco sauce on top covering the tostadas. Sprinkle with remaining 1 cup cheese.
Bake for 35-40 minutes or until bubbly around the edge and the cheese is melted and golden.
Rest for 5-10 minutes then cut into wedges and serve topped with lettuce, pico de gallo, sour cream and cubed avocado.