Halve both grapefruits. Juice as needed to get 1/4 cup freshly squeezed grapefruit juice, then peel the rest. Separate into segments, then cut each segment in half.
Whisk together the grapefruit juice, salt, mustard, red wine vinegar, and honey. While continuing to whisk, pour in the olive oil.
Toss together the salad greens, grapefruit segments, chicken, and walnuts. Pour the vinaigrette over, and toss again. Sprinkle on the cilantro, add some freshly cracked pepper, and enjoy!