Make the lemon-herb dressing: In a bowl or jar combine 60 ml (4 tbsp) extra-virgin olive oil, 60 ml (4 tbsp) fresh lemon juice, minced garlic, chopped parsley, dried oregano, 1/2 tsp salt and a few grinds of black pepper. Whisk or shake to emulsify. Making the dressing first lets the flavors meld and gives you a single seasoned liquid you can both marinate the chicken with and dress the salad — efficient and flavor-forward.

Marinate the chicken briefly: Reserve about 2 tbsp of the dressing for the finished salad (cover and chill), then pour the remaining dressing over the chicken breasts in a shallow dish. Turn to coat, and let sit for 10–15 minutes at room temperature. The lemon and oil lightly tenderize and flavor the meat; you don't need a long marinade because the chicken pieces are thin (150 g each).

Heat your grill pan or outdoor grill over medium-high heat (about 400°F / 200°C). Lightly oil the grate or pan. Bringing the surface to high heat ensures rapid searing which creates a caramelized crust that enhances flavor via the Maillard reaction and helps lock juices inside the chicken.

Pat the chicken quickly with paper towel to remove excess moisture (this promotes browning). Season any exposed areas with a pinch of salt and pepper. Place the breasts on the hot grill or pan. Cook 4–6 minutes per side depending on thickness — you want a deep golden color. Use an instant-read thermometer to check doneness: 74°C / 165°F in the thickest part. Searing first then checking temperature prevents overcooking while ensuring food safety.

Rest and slice the chicken: Transfer the cooked chicken to a cutting board and let rest 5–7 minutes. Resting allows the muscle fibers to reabsorb juices so the meat stays moist when you slice. Slice across the grain into 5–7 mm (1/4–1/3 inch) strips for pleasing bite-sized pieces.

Warm or cool the quinoa: If your cooked quinoa is chilled, gently reheat in a saucepan with a splash of water or briefly in the microwave until just warm — warm quinoa will marry better with the dressed leaves and warm chicken. If you prefer a completely chilled salad, skip reheating. Fluff quinoa with a fork to separate grains (this prevents clumps).

Prepare vegetables and avocado: Halve the cherry tomatoes, slice the cucumber, and thinly slice the avocado. To prevent avocado browning and add brightness, toss the slices lightly with a squeeze of reserved lemon juice from the dressing as soon as you cut them. Acid slows enzymatic browning and adds a fresh note.

Assemble the salad: In a large shallow bowl or platter layer the mixed greens (200 g) first, scatter the warm quinoa evenly, then add halved cherry tomatoes, cucumber, avocado slices and crumbled feta. Arrange sliced grilled chicken on top for a composed look — stacking ingredients differently changes the eating experience, so composing the chicken on top keeps it warm and visually appealing.

Dress and toss gently: Drizzle the reserved dressing evenly over the salad (about half of what you set aside — you can add more to taste). Toss gently with tongs — especially around the avocado — to coat everything without mashing delicate pieces. Tasting as you go prevents overdressing; you can always add more but you can't take it away.

Finish and serve: Scatter a little extra chopped parsley, a grind of black pepper and an optional pinch of flaky sea salt over the top. Serve immediately while the chicken is still warm. If serving later, keep dressing separate and add just before serving to prevent sogginess.