Preheat an outdoor grill for medium-high heat and lightly oil the grate.
Drizzle chicken with 2 tablespoons olive oil; season with salt and pepper. Grill chicken until no longer pink in the center and the juices run clear, 6 to 8 minutes per side. An instant-read thermometer inserted into the center should read at least 165 degrees F (74 degrees C). Place chicken on a flat work surface and slice crosswise into strips.
Place orange juice, 1/2 cup olive oil, tomatillos, shallot, jalapeno, vinegar, cilantro, 1/2 teaspoon salt, and 1/4 pepper in a blender. Puree until dressing is smooth.
Place salad greens in a bowl. Drizzle dressing on top. Add chicken, peaches, avocados, and mint. Crumble dried oranges and sprinkle over the salad.