Toast and cook the quinoa: Rinse 1 cup dry quinoa thoroughly under cold water to remove the bitter saponin coating (this improves flavor and prevents bitterness). Drain. In a medium saucepan, combine rinsed quinoa and 1 3/4 cups water (or low-sodium chicken stock) and a pinch (1/4 tsp) of salt. Bring to a boil over medium-high heat, then reduce to a low simmer, cover tightly and cook for 12–15 minutes until the liquid is absorbed. Remove from heat and let rest, covered, for 10 minutes — this steaming step makes the grains fluffy and separates the kernels rather than leaving them gummy. Fluff with a fork and spread on a tray to cool slightly for the salad.

Make the lemon-herb marinade for the chicken: In a bowl whisk together 2 tbsp extra-virgin olive oil (from the dressing total), 2 tbsp fresh lemon juice, 1/2 tsp garlic powder, 1 tsp lemon zest (if using), 1 tsp kosher salt and 1/4 tsp freshly ground black pepper, plus 2 tbsp chopped parsley. Marinating briefly (15–30 minutes) brightens the chicken with acid and oil: the acid flavors and the oil helps transfer aromatics and keep the meat moist during grilling. If you have time, marinate up to 2 hours in the refrigerator for more flavor penetration.

Prepare the chicken for cooking: Pat the chicken breasts dry with paper towels (dry skin aids browning). If breasts are unevenly thick, butterfly or gently pound them to an even thickness (~1 inch) so they cook evenly and finish at the same time. Place the chicken in the bowl with the marinade, turning to coat; let rest while you prepare vegetables (or refrigerate per the timing above).

Heat the grill or skillet: Preheat an outdoor grill to medium-high (about 400°F / 200°C) or warm a heavy skillet/griddle over medium-high heat with 1 tbsp olive oil. A properly preheated surface gives a quick sear that develops the caramelized golden-brown crust and those flavor compounds (Maillard reaction) without overcooking the interior.

Cook the chicken: Remove excess marinade (shake off but do not wipe) and place the breasts on the hot grill or skillet. Cook for about 4–6 minutes per side for medium-thick breasts, flipping once — you’re aiming for an internal temperature of 74°C / 165°F. Rest the chicken for 5–7 minutes after cooking; resting lets the juices redistribute so slices remain moist rather than leaking onto the cutting board.

While the chicken cooks, assemble the vegetables: In a large mixing bowl combine the cooled, fluffed quinoa, diced cucumber, halved cherry tomatoes, thinly sliced red onion, crumbled feta, and chopped parsley. Toss gently so the ingredients are evenly distributed — contrasting textures (soft cooked quinoa, crunchy cucumber, creamy feta) are the heart of this dish.

Make the dressing: In a small jar or bowl whisk together the remaining 2 tbsp olive oil from the marinade allocation + remaining 2 tbsp olive oil (for the dressing total 4 tbsp), remaining 2 tbsp lemon juice, 1/2 tsp garlic powder, 1/4 tsp kosher salt and a generous pinch of black pepper. Whisking emulsifies the oil and lemon, coating the quinoa and vegetables so each bite has balanced acidity and fat. Taste and adjust: more lemon for brightness, more oil for silkiness, or a pinch of salt to lift flavors.

Dress and toss the salad: Pour about three-quarters of the dressing over the quinoa-vegetable mixture and toss gently to combine — start with most of the dressing and add more if required to avoid a soggy salad. Reserve the remaining dressing to drizzle over plated portions if desired. Adjust seasoning with salt and pepper; the feta is salty, so taste before adding more salt.

Slice the rested chicken: Slice the chicken breasts across the grain into 1/4-inch (6 mm) slices — cutting across the grain shortens muscle fibers and makes each bite tender. Arrange slices on top of (or alongside) the dressed quinoa salad and drizzle any resting juices or reserved dressing over the chicken for shine and flavor.

Serve and finish: Garnish with extra chopped parsley and lemon wedges. Serve slightly warm or at room temperature — the quinoa holds up well, and the lemon-herb notes are most vibrant right away. Leftovers keep well refrigerated for 2–3 days.