Step 1

Preheat the oven to 425ºF and position a rack in the center. Rub a sheet pan with about a teaspoon of neutral oil. Place cauliflower florets and onion on top. Season all over with a teaspoon of kosher salt and pepper to taste, and 3 tablespoons of the oil.

Step 2

In a small bowl, stir together the cumin, coriander, smoked paprika, and cayenne. (If using whole seeds, see notes above.) Pour half (about 1 tablespoon and a scant teaspoon) of this mixture over the cauliflower. Use your hands to toss the cauliflower and onions evenly with the oil and spice mix. Transfer pan to the oven and roast for about 30 minutes, tossing once after about 20 minutes.

Step 3

Meanwhile, place chicken thighs in a large bowl. Season all over with salt (at least another teaspoon). Add the remaining spice mix, remaining 2 tablespoons of oil, and minced garlic. Toss to coat. Let sit at room temperature while vegetables roast.

Step 4

Remove the sheet pan from the oven. Toss everything around. Nestle the thighs around the vegetables. Return pan to the oven and cook for 10 minutes—if thighs are large, they may need 5 more minutes or so. Cut into one to check. Remove pan from the oven and let everything rest on the sheet pan for 10 minutes.

Step 5

Meanwhile, stir together the yogurt sauce (see notes), warm up some bread, cut the lemons, etc. When chicken has rested, transfer it to a platter to cut or cut directly on the sheet pan, taking care not to ruin your pan. The chicken should be in 1- to 2-inch cubes or so—about the same size as the cauliflower. Return chicken to sheet pan or to a serving platter along with the cauliflower. Toss everything together. Taste. Adjust with more salt and pepper if necessary and squeeze a lemon over everything, if desired. To serve, spread flatbread with yogurt sauce, nestle chicken and cauliflower inside, and eat taco-style. Alternatively, serve the flatbread on the side and eat with a knife and fork. Serve lemon wedges on the side.