Prepare the Beef:
Heat a skillet over medium heat. Add the ground beef and cook, breaking it up with a spoon, until browned.
Drain excess fat, then stir in the taco seasoning and water. Simmer for 3-5 minutes until the mixture thickens.
Prepare the Tostada Shells:
If using store-bought shells, warm them in the oven for a few minutes.
For homemade shells, lightly brush corn tortillas with oil and bake at 375°F for 8-10 minutes, flipping halfway, until golden and crispy.
Assemble the Tostadas:
Spread a layer of warmed refried beans on each tostada shell.
Add a scoop of the seasoned beef on top of the beans.
Layer with shredded lettuce, diced tomatoes, shredded cheese, and red onion.
Garnish and Serve:
Drizzle with sour cream or crema. Add optional toppings like sliced jalapeños, avocado, or a sprinkle of cilantro.
Serve immediately to maintain the crunchiness of the shell.