Bring 2 cups water to a boil (or use low-sodium chicken broth for extra flavor). Rinse 1 cup dry quinoa in a fine mesh sieve under cold water until water runs clear to remove the natural saponin coating that can taste bitter. Add rinsed quinoa to the boiling water, reduce heat to a gentle simmer, cover and cook for 12–15 minutes until the liquid is absorbed. Remove from heat and let sit, covered, 5–10 minutes—this resting step lets steam finish cooking the grains and yields fluffy, separate quinoa rather than gummy.

While the quinoa cooks, prep the vegetables: cut the red bell pepper into 1/2" strips and halve lengthwise, and slice the zucchini into 1/2" half-moons. If your red onion is already roasted, roughly chop it into bite-sized wedges; if it needs roasting, toss the whole small red onion (peeled and quartered) with 1/2 tbsp oil, a pinch of salt and roast as below. Toss the pepper and zucchini with 1/2 tbsp olive oil, a pinch of salt and pepper. Coating the vegetables lightly with oil helps them brown and develop sweet roasted flavors rather than steaming.

Roast the vegetables: preheat your oven to 425°F (220°C). Spread the pepper and zucchini in a single layer on a rimmed baking sheet; if you re-roast the onion, add it too. Roast for 18–22 minutes, turning once halfway through, until edges are caramelized and vegetables are tender. High heat encourages Maillard browning which concentrates sweetness and adds savory depth.

Marinate the chicken briefly while the quinoa and vegetables cook: pat the 12 oz chicken breasts dry (drying promotes browning), then drizzle with 1/2 tbsp olive oil, the juice of 1/2 lemon (about 1 tbsp), 1/4 tsp salt, 1/8 tsp black pepper and (optional) 1/4 tsp dried oregano or thyme. Let sit at room temperature for 10–15 minutes while other elements finish — this short marinade brightens flavor and helps the chicken take on the lemon-herb profile without making it mushy.

Grill the chicken: preheat a grill pan or outdoor grill to medium-high (about 425°F). Oil the grates lightly to prevent sticking. Grill chicken 5–7 minutes per side (depending on thickness) until the internal temperature reaches 165°F (74°C). Letting the chicken come to room temperature before grilling shortens cook time and promotes even cooking. Searing on high heat develops a golden crust and adds flavor; finish at moderate heat so it cooks through without burning.

Rest and slice the chicken: remove chicken from the grill and tent loosely with foil for 5 minutes. Resting allows juices to redistribute so slices remain moist. Slice the breasts into 1/4" thick slices across the grain for the most tender bite.

Assemble the dressing: in a small bowl whisk the remaining 1 tbsp olive oil, remaining lemon juice (juice of 1/2 lemon ≈ 1 tbsp), minced garlic (optional), a pinch of salt and freshly ground black pepper. Whisking emulsifies the oil and lemon, coating the quinoa and greens evenly and brightening flavors.

Finish the quinoa: fluff the rested quinoa with a fork to separate the grains (this keeps the salad light). While still warm, toss the quinoa with the roasted vegetables, chopped roasted red onion, half of the dressing, and a pinch more salt and pepper to taste. Warm quinoa absorbs dressing more readily and melds flavors together.

Plate the salad: arrange 1 cup mixed salad greens per plate (or bowl), spoon half the quinoa-roasted vegetable mixture over the greens, and fan sliced grilled chicken across the top. Drizzle with the remaining dressing and finish with a grind of black pepper and, if you like, a small pat of butter on the hot chicken for extra gloss and richness.

Serve immediately while the chicken is warm and the quinoa is slightly warm; this contrast with cool greens creates great texture. Leftovers store well in the fridge for up to 3 days (keep dressing separately if possible to maintain greens texture).