Preheat your oven to 425°F or heat a skillet over medium-high heat with a drizzle of vegetable oil. If baking, lightly spray each corn tortilla with cooking spray and place them on a baking sheet. Bake for about 4 minutes on each side, flipping them once until they turn golden brown and crispy. Set them aside on a wire rack to maintain their crunch.

In a large skillet, sauté lean ground beef over medium-high heat for about 6-8 minutes, breaking it up with a spoon as it cooks. Add diced yellow onion and continue cooking until the onion becomes translucent, around 3-4 minutes. Season the mixture with taco seasoning, garlic powder, and salt, stirring well to distribute the flavors.

While the beef is cooking, warm your refried beans in a small saucepan over low heat for about 5 minutes, stirring occasionally to prevent sticking. Alternatively, you can microwave them in a bowl for about 1-2 minutes until heated through.

Start assembling your tostadas by spreading a generous layer of warmed refried beans on each crispy tortilla. Next, pile on the cooked ground beef mixture evenly across the tortillas, followed by a handful of shredded iceberg lettuce, diced tomatoes, and creamy avocado slices. Add a spoonful of pico de gallo or salsa for an extra burst of flavor.

To finish your easy tostadas, crumble cotija cheese over the top and sprinkle with fresh cilantro if desired. Serve immediately while the tostadas are still warm and crispy.