Adjust rack to top position (top and middle positions for 4 servings) and preheat oven to 450 degrees. Wash and dry produce.

Trim and halve zucchini lengthwise; cut crosswise into ¼-inch-thick half-moons. Halve, core, and thinly slice green pepper into strips. Thinly slice tomato into rounds.

Heat a large drizzle of oil in a large pan over medium-high heat. Add zucchini, half the garlic powder, and a pinch of salt and pepper. Cook, stirring occasionally, until zucchini is lightly browned, 2-3 minutes. Turn off heat; transfer to a plate. Wipe out pan.

Heat another drizzle of oil in same pan over medium-high heat. Add green pepper and a pinch of salt and pepper. Cook, stirring occasionally, until lightly browned, 2-3 minutes.

Meanwhile, place flatbreads upside down (dimple sides down) on a baking sheet. Drizzle both sides of each flatbread with olive oil; brush or rub to coat all over and season with salt and pepper.

Toast on top rack until golden brown, 3-5 minutes. (For 4 servings, divide flatbreads between two baking sheets; toast on top and middle racks, swapping rack positions halfway through toasting.) TIP: If you added any other items to your meal (apps, sides, and/or dessert), you can get started on them now!

Place tomato, zucchini, green pepper, marinara, and mozzarella in separate serving vessels. Present toppings family style with toasted flatbreads (dimpled sides up) for everyone to build their own pizzas. (You’ll bake the pizzas in the next step!)

Bake flatbread pizzas on top rack until cheese melts and flatbreads are crispy, 4-6 minutes. (For 4 servings, divide flatbread pizzas between two baking sheets; bake on top and middle racks, swapping rack positions halfway through.)

Meanwhile, in a large bowl, whisk together half the balsamic glaze, 1 TBSP olive oil (2 TBSP for 4 servings), and a pinch of salt and pepper. Add arugula; toss to combine.

Slice flatbread pizzas into pieces. Divide flatbreads and salad between plates.

Place ranch dressing, remaining balsamic glaze, and remaining garlic powder in serving bowls. Serve alongside flatbread pizzas, with walnuts on the side to garnish salad as you like. (Don't forget to serve with any extra items you may have ordered to build out your meal!)