Pat chicken dry using paper towels and place in large resealable plastic bag. (Lightly pound or butterfly chicken to an even 3/4-inch thickness.) Combine oil, lime peel, lime juice, jalapenos, garlic and cumin in a small bowl; add to chicken. Marinate for 15 to 30 minutes or refrigerate overnight.
Remove chicken from marinade and discard marinade. Preheat grill to medium heat or about 350°F. Grill chicken for 4 to 6 minutes per side or until cooked through. Remove from grill.
To make Tomatillo Avocado Sauce: heat oil in a saucepan over medium-high heat. Stir in onions and sauté for 2 to 3 minutes or until softened. Stir in garlic and continue cooking for 1 minute.
Remove from heat and pour into blender or food processor. Add tomatillos, avocado, green chilies, jalapenos, cumin, bouillon and cilantro. Pulse 4 or 5 times or until pureed; add water until desired consistency is reached.
Serve over grilled chicken and garnish cilantro and lime wedges, if desired.
Recipe Note: Fresh tomatillos can be found in the produce section of most grocery stores and Latin markets. For a more spicy sauce, add 1 or 2 chopped, fresh serrano or jalapeno chile peppers and sauté them with the onions.