Add the sliced red onion to a small bowl with the red wine vinegar, sugar, and 1/2 teaspoon of the kosher salt from the spice blend. Toss well and set aside — it will soften and turn bright pink while you cook.

Stir together all the shawarma spice blend ingredients in a small bowl. Pat the chicken strips dry with paper towels, drizzle with 1 tablespoon of the olive oil, and toss with the spice blend until every strip is evenly coated.

Heat the remaining 1 tablespoon olive oil in a large skillet over medium-high heat until shimmering. Add half the chicken strips in a single layer — don't crowd — and sear undisturbed for 3–4 minutes per side, until deeply browned at the edges and cooked through. Transfer to a plate and repeat with the remaining chicken.

Prepare the instant basmati rice according to package directions (typically: boil water, stir in rice, cover, rest 5 minutes). If using ready-rice pouches, microwave per package directions. Fluff with a fork.

Whisk the Greek yogurt, grated garlic, lemon juice, olive oil, and salt in a small bowl. Thin with water a tablespoon at a time until it drizzles easily off a spoon. Taste and add more lemon or salt if needed.

Let the chicken rest 2 minutes, then slice any larger strips bite-size. Divide the rice among 4 bowls. Top with the shawarma chicken, a tangle of pickled onion, cucumber, and cherry tomatoes. Drizzle generously with garlic yogurt sauce, scatter with parsley, and serve with lemon wedges and feta if using.