Bring your mise en place together: halve the cherry tomatoes, seed and dice the cucumber and red pepper, crumble the feta, and finely chop the parsley. Having everything prepped makes assembly fast and keeps ingredients at their freshest (especially important for vegetables that can weep once salted).

Rinse the dry quinoa in a fine-mesh sieve under cold running water for 30–60 seconds, rubbing the grains with your fingers. Rinsing removes the natural bitter coating (saponin) and gives a cleaner, brighter flavor.

Toast the rinsed quinoa (optional but recommended): place a medium saucepan over medium heat, add the quinoa and toast, stirring, for 2–3 minutes until it smells nutty. Toasting deepens the flavor so the cooked quinoa tastes more complex and 'toasted' rather than flat.

Add 2 2/3 cups (≈640 ml) water and 3/4 tsp kosher salt to the saucepan. Bring to a boil, then reduce to a gentle simmer, cover and cook for 12–15 minutes, until the water is absorbed and the germ has unfurled. Turn off the heat and let the quinoa rest, covered, for 5 minutes to finish steaming — this makes it light and fluffy rather than gluey.

While the quinoa cooks, prepare the chicken: pat the breasts dry (this helps develop a good crust), then rub with 1 tbsp olive oil, 3/4 tsp kosher salt and 1/4 tsp black pepper. If using, sprinkle 1 tsp za'atar or 1 tsp dried oregano over the chicken and rub it in. The oil helps the seasoning adhere and encourages a golden sear.

Preheat a grill or a heavy grill pan to medium-high (about 200–230°C / 400–450°F). A hot surface sears quickly, creating Maillard browning that adds savory, roasted flavor. If grilling outdoors, oil the grates lightly to prevent sticking.

Grill the chicken 4–6 minutes per side depending on thickness, flipping once — you want good color and char but avoid overcooking. Cook to an internal temperature of 74°C (165°F) measured at the thickest part; alternatively, remove at ~71°C (160°F) and rest to reach 74°C by carryover. Rest the chicken for 6–8 minutes under loose foil — resting lets the juices redistribute so the chicken stays moist when sliced.

While the chicken rests, transfer the cooked quinoa to a large mixing bowl and fluff with a fork to separate the grains. Fluffing prevents clumping and keeps the salad texture lively.

Make the lemon dressing: in a small bowl whisk together 4 tbsp fresh lemon juice, 3 tbsp extra-virgin olive oil, remaining 1 tbsp olive oil (reserved for finishing), 1/2 tsp black pepper and a pinch of kosher salt (about 1/2 tsp). Whisking emulsifies the lemon and oil so the dressing clings to the quinoa and vegetables instead of pooling at the bottom.

Add the halved cherry tomatoes, diced cucumber, diced red pepper and chopped parsley to the fluffed quinoa. Toss gently with about two-thirds of the dressing to coat — you can add more later. Mixing while the quinoa is still slightly warm allows it to absorb flavor from the dressing.

Slice the rested chicken thinly on a bias (against the grain) — this creates tender, easy-to-bite pieces and looks elegant on the plate. Add sliced chicken and crumbled feta to the quinoa-vegetable mixture and toss gently to combine. Taste and adjust salt, pepper or lemon as needed.

Plate the salad: divide among four bowls or plates, drizzle with the remaining dressing (and an optional extra drizzle of olive oil), and finish with a few grinds of black pepper and a small sprinkle of za'atar or oregano if desired. Serve at room temperature or slightly chilled — both are excellent.