01 - Preheat oven to 400°F (200°C). Lightly brush both sides of the corn tortillas with vegetable oil. Arrange them on baking sheets and bake for 5–7 minutes per side, or until they become crispy and golden. Remove from oven and set aside.
02 - Heat 1 tablespoon of vegetable oil in a large skillet over medium heat. Add the finely diced onion and cook until softened, approximately 3 minutes. Stir in the minced garlic and continue cooking for 30 seconds.
03 - Add the ground beef to the skillet, breaking it up with a spoon. Cook until the beef is thoroughly browned and cooked through, about 6–8 minutes. If necessary, drain off any excess fat.
04 - Stir in the chili powder, ground cumin, smoked paprika, dried oregano, salt, and black pepper. Mix thoroughly to ensure all spices are well incorporated with the beef.
05 - Add the tomato sauce and water to the skillet. Bring the mixture to a simmer and cook for 3–4 minutes, stirring occasionally, until the sauce slightly thickens. Remove the skillet from the heat.
06 - To assemble, spread a generous spoonful of the seasoned beef mixture onto each crispy tostada shell.
07 - Top the beef-laden tostadas with shredded lettuce, diced tomatoes, shredded cheddar or Mexican blend cheese, sour cream, avocado slices, chopped fresh cilantro, and sliced black olives, according to preference.
08 - Serve the beef tostadas immediately while the shells are crisp to enjoy their optimal texture.