• Place a foil-lined baking sheet on top rack (for 4 servings, use 2 foil-lined sheets on top and middle racks) and preheat oven to 450 degrees. Wash and dry produce. • Halve, peel, and thinly slice onion. Drain pineapple over a small bowl, reserving juice. Stir 1/4 of the onion, half the vinegar (you’ll use the rest later), and a pinch of salt into bowl with juice. Set aside.

• Heat a drizzle of oil in a large pan over medium heat. Add remaining onion; cook, stirring and adding splashes of water as needed to prevent sticking, until softened, 6-8 minutes. While onion cooks, rinse shrimp under cold water; pat dry with paper towels. Heat a drizzle of oil in a second large pan over medium heat. Add shrimp or beef in a single layer and season all over with salt and pepper. Cook, stirring frequently, until cooked through, 3-5 minutes for shrimp or 4-6 minutes for beef.

• While onion cooks, halve, core, and very thinly slice green pepper into strips. Toss in a second small bowl with a drizzle of olive oil, salt, and pepper. Dice mozzarella into 1/2-inch pieces. Finely chop cilantro.

• Once cooked onion is softened, increase heat under pan to medium high. Add pineapple and a drizzle of oil; cook, stirring, until pineapple is lightly browned, 2-3 minutes. • Stir in remaining vinegar. Cook, stirring, until onion and pineapple are caramelized and jammy, 1-2 minutes more. Turn off heat and season with salt and pepper.

• Brush or rub each flatbread with a drizzle of oil. Carefully remove prepared baking sheet from oven; place flatbreads on sheet. (For 4 servings, divide flatbreads between prepared sheets.) • Evenly spread flatbreads with BBQ sauce, then top with caramelized onion and pineapple, green pepper, Monterey Jack, and mozzarella. Top flatbreads with shrimp or beef after adding mozzarella.

• Return flatbreads to top rack until cheese melts and edges are golden brown, 10-12 minutes. (For 4 servings, return to top and middle racks; swap rack positions halfway through baking.) • Transfer flatbreads to a cutting board and top with cilantro and pickled onion (draining first) to taste. Cut into pieces, divide between plates, and serve. Ground Beef is fully cooked when internal temperature reaches 160°.