Preheat oven to 450 degrees. Wash and dry all produce. Halve, peel, and thinly slice onion. Halve and core pear. Thinly slice one half; dice other half. Heat a drizzle of oil in a large pan over medium heat. Add onion and sliced pear and cook, stirring, until browned, 7-9 minutes.

Once onion and pear are browned, stir half the vinegar and 1 tsp sugar into pan. Let reduce until syrupy, 1-2 minutes more. Season with salt and pepper. Remove from pan and set aside in a small bowl. Wipe out pan.

Tear mozzarella into small pieces. Place flatbreads on a baking sheet. Evenly sprinkle with mozzarella and topping. Bake until mozzarella melts and flatbreads are golden brown, 10-12 minutes.

While flatbreads bake, heat 2 TBSP olive oil and a pinch of chili flakes (about 1/4 tsp) in pan used to cook topping over medium-high heat. Once oil is hot and begins to bubble slightly, 1-2 minutes, immediately turn off heat. Pour chili oil into a small bowl and let cool.

In a large bowl, toss together lettuce, diced pear, a drizzle of olive oil, and 1 tsp vinegar. Season with salt, pepper, and more vinegar (to taste).

Cut baked flatbreads into slices and drizzle with chili oil to taste. (TIP: For less heat, strain out the chili flakes using a fine-mesh strainer.) Serve with salad on the side.