Step 1: If making homemade tostada shells, preheat your oven to 375°F (190°C). Lightly brush corn tortillas with olive oil on both sides. Arrange on a baking sheet and bake for 5-7 minutes per side, or until golden brown and crispy. Set aside.
Step 2: In a medium saucepan or microwave-safe bowl, combine the shredded cooked chicken and BBQ sauce. Heat over medium-low heat on the stovetop, stirring occasionally, until the chicken is heated through and well coated in the sauce (about 5-7 minutes). Alternatively, microwave in 30-second intervals, stirring, until hot.
Step 3: Lay out the crispy tostada shells on a serving platter or individual plates. If desired, you can warm the store-bought tostada shells in the oven for a few minutes to enhance crispness.
Step 4: Spoon a generous amount of the warm BBQ chicken mixture evenly over each tostada shell.
Step 5: Sprinkle each tostada with shredded cheddar cheese, diced red onion, and chopped fresh cilantro.
Step 6: Top with optional additions like diced avocado, a dollop of sour cream or Greek yogurt, and sliced jalapeños for extra flavor and freshness. Serve immediately with lime wedges on the side, if desired.