Prepare the chicken and marinade: Pat the chicken breasts dry with paper towels (this helps create a good sear). In a shallow bowl, whisk together 1 tablespoon extra-virgin olive oil, 1/2 tablespoon balsamic vinegar, 1/2 tsp kosher salt, 1/4 tsp freshly ground black pepper, and 1 minced garlic clove. Add half of the torn basil (reserve the rest for finishing). Coat the chicken in the marinade and let sit at room temperature for 10–15 minutes. Why: Marinating briefly seasons the surface and the oil helps transmit heat evenly for better browning; bringing the chicken slightly toward room temperature shortens cooking time and prevents overcooking the exterior while the interior comes up to temperature.

Heat the grill or a heavy grill pan: Preheat an outdoor grill or a stovetop cast-iron grill pan over medium-high heat until very hot (about 5 minutes). Oil the grates or pan lightly with a brush of oil. Why: A hot cooking surface gives immediate contact heat and creates the characteristic char and Maillard flavor — that flavor is a major component of the dish’s appeal.

Grill the chicken: Place the chicken on the hot grill. Sear without moving for 3–4 minutes to develop a golden-brown crust, then flip and grill another 3–4 minutes. Use an instant-read thermometer to check for doneness: the internal temperature should read 160–165°F (71–74°C). Why: Searing seals flavor and creates texture; checking temperature prevents drying out — remove at 160°F and rest (carryover will bring it to 165°F).

Rest and slice the chicken: Transfer chicken to a cutting board and tent loosely with foil; rest for 5–7 minutes. Then slice the breasts thinly against the grain. Why: Resting redistributes juices so the meat stays moist; slicing against the grain shortens muscle fibers and yields tender bites.

Make the dressing: In a small bowl, whisk together 2 tablespoons extra-virgin olive oil, 1 1/2 tablespoons balsamic vinegar, the remaining 1/2 tsp kosher salt, remaining 1/4 tsp black pepper, the thinly sliced or minced garlic clove, and a small pinch of sugar if your balsamic is very tart (optional). Taste and adjust for balance — it should be bright with a soft acidity. Why: Whisking emulsifies the oil and vinegar so the dressing clings to the arugula and tomato, giving even flavor in every bite.

Dress the greens and build the salad base: Place the arugula in a large bowl, add the halved cherry tomatoes and thin red onion slices. Drizzle about two-thirds of the dressing and toss lightly to coat. Why: Tossing the greens with most of the dressing first ensures the leaves are properly flavored without saturating them; arugula is delicate and can wilt if over-dressed.

Assemble the salad: Arrange the dressed arugula and tomatoes on a serving platter or divide between two plates. Fan the sliced avocado over the greens, scatter the Kalamata olives, and lay the sliced grilled chicken across the top. Drizzle the remaining dressing over the chicken and avocado. Finish with torn basil leaves and a light grind of black pepper. Why: Layering components keeps textures distinct — warm chicken over cool greens is an excellent contrast; finishing with fresh basil brightens the whole plate.

Final adjustments and serve: If desired, finish with a quick drizzle (about 1 teaspoon) of extra-virgin olive oil for gloss and richness. Serve immediately while the chicken is warm. Why: Serving right away preserves the contrast between warm protein and crisp greens; the little finish oil adds silky mouthfeel and glossy presentation.