Place a lightly oiled baking sheet on top rack (2 lightly oiled baking sheets on top and middle racks for 4 servings) and preheat oven to 450 degrees. Wash and dry produce.

Core, deseed, and dice green pepper into ½-inch pieces.

Open package of chicken* and drain off any excess liquid.

Heat a large drizzle of oil in a large pan over medium-high heat. Add chicken and green pepper; season with salt and pepper. Cook, stirring, until chicken is browned and cooked through, 4-6 minutes.

Stir in BBQ sauce, then remove pan from heat.

Meanwhile, carefully place flatbreads on preheated sheet. Drizzle both sides of each flatbread with olive oil and season with salt and pepper. (For 4 servings, divide flatbreads between both preheated sheets. Toast on top and middle racks; swap rack positions halfway through toasting.)

Toast on top rack until golden brown and crisp, 3-4 minutes.

Evenly top toasted flatbreads with BBQ chicken mixture, mozzarella, and cheddar.

Return to oven until cheese melts, 2-3 minutes. Transfer to a cutting board and slice each flatbread into quarters.

Divide flatbreads between plates. Drizzle with ranch dressing and serve.