Pat the chicken dry and place on a cutting board. Rub with 1 tablespoon olive oil, 1/2 teaspoon salt, 1/2 teaspoon pepper and 1/4 teaspoon garlic powder. Set aside while you prepare the rest of the salad (about 5–10 minutes).
Make the dressing: whisk together Greek yogurt, honey, apple cider vinegar, olive oil, poppy seeds, lemon zest and Dijon in a small bowl until smooth. Taste and season with a pinch of salt and pepper; set half aside for tossing and reserve the rest for drizzling at the table.
Heat a large skillet over medium-high heat until hot. Add the chicken and cook undisturbed 6–7 minutes, then flip and cook another 6–7 minutes until an instant-read thermometer reads 160–165°F. (Timing will vary with thickness.)
Transfer chicken to a plate and loosely tent with foil; let rest 6–8 minutes to finish cooking and keep juices locked in. While the chicken rests, toss spinach, sliced strawberries, toasted pecans, crumbled feta and sliced red onion in a large bowl.
Slice the rested chicken thinly against the grain. Add the warm chicken to the salad bowl and drizzle with half of the prepared dressing; toss gently to coat so the heat slightly softens the strawberries and wilts the greens for a balanced texture.
Divide the salad among plates or large bowls, scatter any remaining pecans and feta, then finish with a light drizzle of the reserved dressing and a little extra black pepper if desired. Serve immediately.