Step 1: Prepare the Chicken. Trim any excess fat from the chicken breasts. If very thick, pound them gently to about 3/4-inch thickness. In a shallow dish or zip-top bag, combine chicken with 1 tablespoon olive oil, chili powder, garlic powder, salt, and pepper. Massage to coat. Marinate for 15-30 minutes at room temperature, or up to 2 hours in the refrigerator.
Step 2: Grill the Chicken. Preheat your grill to medium-high heat (about 400°F/200°C). Lightly oil the grill grates. Place the marinated chicken breasts on the hot grill. Cook for 5-7 minutes per side, or until internal temperature reaches 165°F (74°C) and chicken is nicely charred. Remove from grill and let rest on a cutting board for at least 5 minutes before slicing.
Step 3: Grill the Peaches. While chicken is resting, slice each pitted peach half into 3-4 wedges. Lightly brush peach wedges with olive oil. Place them on the grill, cut-side down, and cook for 2-3 minutes per side, just until grill marks appear and they begin to soften slightly but still hold their shape.
Step 4: Make the Vinaigrette. In a small bowl, whisk together the fresh lime juice, honey, remaining 2 tablespoons of olive oil, and a pinch of salt and pepper until well combined and slightly emulsified. Taste and adjust seasonings as needed.
Step 5: Assemble the Salad. In a large serving bowl, combine the mixed greens, thinly sliced red onion, and diced avocado. Slice the rested grilled chicken into strips and add to the bowl along with the grilled peach wedges. Crumble the feta cheese over the top.
Step 6: Dress and Serve. Drizzle the honey-lime vinaigrette over the entire salad. Toss gently to combine all ingredients. Serve immediately and enjoy your vibrant, fresh salad!