Step 1: If starting with raw chicken, cook, shred, and then toss with BBQ sauce. If using pre-cooked chicken, simply toss the shredded chicken with BBQ sauce in a medium bowl until well coated. You can gently warm the chicken mixture in a saucepan over low heat for 5 minutes, or serve it at room temperature.
Step 2: Prepare your toppings. Shred the lettuce, dice the tomato, slice or dice the avocado, crumble the cotija cheese, and chop the cilantro. Set all toppings aside in individual bowls.
Step 3: Heat about 1/2 inch of vegetable oil in a large, heavy-bottomed skillet or cast-iron pan over medium-high heat. The oil is ready when a small piece of tortilla sizzles immediately upon contact.
Step 4: Carefully place one or two corn tortillas into the hot oil (do not overcrowd the pan). Fry for 1-2 minutes per side, or until golden brown and crispy. Use tongs to flip them.
Step 5: Remove the crispy tostada shells from the oil and place them on a wire rack lined with paper towels to drain any excess oil. Immediately sprinkle lightly with salt. Repeat with the remaining tortillas.
Step 6: To assemble your bbq chicken tostadas, take a crispy tostada shell and spread a generous layer of the BBQ chicken mixture over it.
Step 7: Top the chicken with shredded lettuce, diced tomato, and sliced or diced avocado.
Step 8: Finish each tostada with a sprinkle of crumbled cotija cheese and fresh cilantro, if desired. Serve immediately with a dollop of sour cream or a squeeze of fresh lime juice, if using. Enjoy your delicious bbq chicken tostadas!