Wash and dry all produce. Adjust racks to middle and upper positions and preheat oven to 450 degrees. Bring a large pot of salted water to a boil. Peel and trim carrots, then slice diagonally into 1/2-inch-thick coins. Halve and peel onion, then cut into 1/2-inch-thick wedges.

Toss carrots and onion on a baking sheet with a drizzle of oil, half the spice blend, and a large pinch of salt and pepper. Pat chicken dry with a paper towel. Rub all over with a drizzle of oil, then season evenly with salt, pepper, and remaining spice blend. Arrange skin-side up on a second baking sheet.

Roast chicken on upper rack and veggies on middle rack until chicken is cooked and veggies are tender, 25-30 minutes. Meanwhile, zest 11/2 tsp zest from lemon, then halve; cut one half into wedges. Trim, then thinly slice scallions, separating greens and whites. Core and finely chop tomato. Mince garlic.

In a small bowl, stir together yogurt, lemon zest, juice from lemon half, half the honey (1 packet), and a pinch of za’atar (save the rest for garnish). Season with salt and pepper. Set aside. Once water boils, add orzo to pot. Cook, stirring occasionally, until al dente, about 9 minutes. Reserve 1/2 cup pasta cooking water, then drain. Keep orzo in strainer and return empty pot to stove.

Heat 1 TBSP butter and a drizzle of olive oil in the same pot over mediumlow heat. Add scallion whites and tomato. Cook, tossing often, until softened, 2-3 minutes. Season with salt and pepper. Add garlic and cook, tossing, until fragrant, about 1 minute. Return orzo to pot along with 1/4 cup pasta cooking water. Stir to combine. (TIP: If mixture seems dry, add more water, a splash at a time, to loosen.) Remove pot from heat.

Stir 1 TBSP butter and a few squeezes of lemon into pot. Season with salt and pepper. Brush or drizzle chicken with remaining honey. Divide orzo, chicken, and veggies between plates. Garnish with scallion greens. Sprinkle with remaining za’atar, if desired. Serve with yogurt sauce and any extra lemon on the side for drizzling.