Assertive feta cheese pairs well with acidic tomatoes and rich avocados in this 5-minute salsa. Make this salsa right before serving, and avoid refrigerating it—the texture of the tomato will soften. Serve this dish with a side of grilled vegetables.
Combine first 4 ingredients in a large heavy-duty zip-top plastic bag. Place chicken between 2 sheets of plastic wrap; pound to 1/4-inch thickness using a meat mallet or small heavy skillet. Sprinkle chicken with salt and pepper, and add to bag; seal. Marinate in refrigerator 30 minutes.
Remove chicken from marinade, discarding marinade. Place chicken on a grill rack coated with cooking spray. Grill 3 minutes on each side or until done.