Before starting, preheat the oven to 450°F. Wash and dry all produce. Pat chicken dry with paper towels. Cover each chicken breast with plastic wrap. Using a mallet, rolling pin or heavy-bottomed pan, carefully pound each chicken breast until 1/2-inch thick. Season with BBQ Seasoning, salt and pepper.

Heat a large non-stick pan over medium heat. When hot, add 1/2 tbsp oil, then chicken. Pan-fry until golden-brown, 1-2 min per side. (NOTE: For 4 ppl, cook chicken in 2 batches, using 1/2 tbsp oil per batch.) Transfer chicken to a parchment-lined baking sheet. Roast in the middle of the oven until cooked through, 8-10 min.** Thinly slice chicken.

While chicken cooks, peel, then cut half the onion into 1/8-inch rounds (whole onion for 4 ppl). Separate into rings. Cut tomato into 1/2-inch pieces. Add vinegar, 1/4 tsp sugar and 1 1/2 tbsp oil (dbl both for 4 ppl) to a large bowl. Season with salt and pepper, then whisk to combine. (NOTE: This is your vinaigrette.) Reserve 2 tbsp BBQ Sauce (dbl for 4 ppl) in a small bowl.

Arrange flatbreads on a foil-lined baking sheet. Evenly spread remaining BBQ sauce across flatbreads. Top with chicken, then onion rings and mozzarella. Bake in the middle of the oven until cheese melts, 6-7 min. (NOTE: For 4 ppl, use two baking sheets and bake in the middle and top of the oven, rotating sheets halfway through.)

Switch oven to broil and move pizzas to the top of the oven. Broil until cheese is golden and flatbread edges are dark-brown, 1-3 min. (NOTE: For 4 ppl, broil one baking sheet of pizzas at a time.)

Add spinach, carrots and tomatoes to the large bowl with vinaigrette. Toss to combine. Drizzle reserved BBQ Sauce over pizzas. Cut pizzas into quarters. Divide pizzas and salad between plates.