Walnut-mushroom flatbreads with apricots and lemon-tahini dressing

Heat the oven to 400°F. 

• Peel and thinly slice enough onion to measure ¼ cup [½ cup]; set aside for assembling the flatbreads. Finely chop the remaining onion.
• Finely chop the walnuts.
• Finely chop the mushrooms.

In a large frying pan over medium heat, warm 1 to 2 tablespoons oil until hot but not smoking. Add the chopped onion and cook, stirring occasionally, until starting to soften, 2 to 4 minutes. Add the walnuts and mushrooms, season with salt and pepper, and cook, stirring occasionally, until the mushrooms start to soften, 2 to 3 minutes. Stir in the tomato sauce and cook until fragrant, about 1 minute.

Add the flatbread spice blend and ¼ cup [½ cup] water and season with salt and pepper. Bring to a boil, reduce to a simmer, and cook, stirring occasionally, until the liquid has almost evaporated, 3 to 5 minutes. Remove from the heat and season to taste with salt and pepper. While the walnut-mushroom topping is cooking, prepare the flatbreads.

• Brush the tops of the flatbreads lightly with oil.

On a sheet pan or directly on the oven rack, place the flatbreads side by side and bake until crisp, 3 to 5 minutes. Meanwhile, prepare the remaining ingredients. 

• Finely chop the apricots.

In a small bowl, stir together the lemon tahini and 2 tablespoons [¼ cup] oil; season to taste with salt and pepper. 

Top the flatbreads with the walnut-mushroom topping, arugula, sliced onion, and apricots, leaving a ½-inch border around the edges. Drizzle with as much lemon-tahini dressing as you like and sprinkle with the sumac (set aside any remaining dressing for serving). Cut into squares.

Transfer the flatbreads to individual plates and serve any remaining dressing on the side.