How to Make It
Combine 2 tablespoons oil and 2 tablespoons vinegar in a large zip-top plastic bag. Add chicken to bag; seal. Let stand 10 minutes, turning occasionally.
Heat a grill pan over medium-high heat. Remove chicken from marinade; discard marinade. Sprinkle chicken with 1/4 teaspoon salt and 1/4 teaspoon pepper. Coat pan with cooking spray. Add chicken to pan; grill 5 minutes on each side or until done. Cut into slices.
Combine remaining 1 tablespoon oil, remaining 1 tablespoon vinegar, remaining 1/4 teaspoon salt, remaining 1/4 teaspoon pepper, and sugar in a large bowl, stirring with a whisk. Add strawberries; toss to coat. Add arugula and onion to strawberry mixture; toss gently to combine. Sprinkle feta over salad. Divide salad among 4 plates; top evenly with sliced chicken.