To prepare vinaigrette: Puree cilantro, oil, lime juice, orange juice, salt, pepper and garlic in a blender or food processor until smooth.
To prepare salad: Slice both ends off oranges. With a sharp knife, remove the peel and white pith; discard. Working over a salad bowl, cut the segments from their surrounding membrane; discard the membrane. Add greens, avocado, onion and vinaigrette; toss to coat. (Refrigerate the extra dressing for up to 2 days.)
Notes
Make Ahead Tip: The recipe makes 1 1/4 cups dressing (Step 1); cover and refrigerate extra dressing for up to 2 days.