Combine the brown sugar, chili powder, cumin, garlic powder, onion powder, paprika, salt, and crushed red pepper flakes in a small bowl, mixing thoroughly to distribute the spices evenly. Pat the chicken tenders dry with paper towels, then toss them with the spice mixture until each piece is well coated. I prefer to let the seasoned chicken sit for a few minutes while I prep the other ingredients—this allows the flavors to start penetrating the meat.

While the chicken is cooking, prepare your assembly ingredients. Dice the pineapple into 1/2-inch pieces and pat them dry with paper towels to remove excess moisture—this prevents soggy flatbread. Thinly slice the red onions into half-moons and have the cilantro ready. Shred the cheese if not already done, and measure out the barbecue sauce. Having everything prepped and within arm's reach makes the final assembly quick and efficient.

Heat your grill or grill pan to medium-high heat and cook the seasoned chicken tenders for 4-5 minutes per side until they develop a golden-brown crust and reach an internal temperature of 165°F. Transfer the cooked chicken to a cutting board and let it rest for 10 minutes—this keeps the meat juicy. After resting, cut the chicken into 1-inch bite-sized chunks. While the chicken rests, preheat your oven to 400°F.

Place the flatbreads on a large baking sheet or pizza pans. Spread each flatbread with a thin layer of barbecue sauce, then distribute the cooked chicken chunks evenly across each one. Sprinkle the shredded cheese over the chicken, then scatter the diced pineapple and sliced red onions on top. I find that patting the pineapple dry really makes a difference—it keeps the flatbread from getting soggy during baking.

Bake the assembled flatbreads at 400°F for 10-12 minutes, until the cheese is melted and bubbly and the edges of the flatbread are lightly golden. Watch for doneness around the 10-minute mark—you want the cheese fully melted but the flatbread still chewy, not crispy.

Remove the flatbreads from the oven and immediately top with fresh cilantro leaves. Drizzle each flatbread lightly with fresh lime juice, which brightens the flavors and cuts through the richness of the cheese and barbecue sauce. Cut each flatbread into slices and serve immediately.