Method:

• In 10-inch skillet, heat oil over medium-high heat until hot. Add garlic and onion; cook about 5 minutes, stirring constantly, until onion is tender.
• Remove husks from tomatilllos; rinse tomatilllos well. Cut around stem area of each to remove core; cut tomatillos into quarters. In large food processor, place garlic and onion, tomatillos, jalapeno chili, cilantro, sugar and 1/2 teaspoon of the salt. Cover; process about 15 seconds or until almost smooth.
• Pour 1 cup tomatillo mixture into small serving bowl; cover and refrigerate to serve as salsa. To make marinade, add remaining 1/2 teaspoon salt and the cumin to remaining mixture in food processor. Cover; process 10 seconds.
• Place chicken breasts in glass baking dish. Spoon marinade over chicken; spread marinade over chicken to coat evenly. Cover with plastic wrap; refrigerate at least 4 hours but no longer than 8 hours, turning chicken at least once while marinating.
• Heat gas or charcoal grill. Carefully brush additional oil on grill rack. Place chicken on grill over medium heat; discard marinade. Cover grill; cook 12 to 15 minutes, turning once, until juice of chicken is clear when center of thickest part is cut (170ºF). Serve each chicken breast with about 2 tablespoons salsa.