In small bowl, mix together lemon juice, garlic, honey, pepper flakes and Adobo. Using whisk, add olive oil in slow steady stream, whisking constantly to combine. Stir in cilantro; set aside.
Heat grill to medium-high heat. (Or, heat oven to 425°F.) On plate, drizzle chicken with olive oil and sprinkle with adobo. Grill chicken, flipping once, until dark golden brown on both sides and cooked through, about 15 minutes. (If cooking in oven, place chicken on foil-lined baking sheet. Cook until golden brown and cooked through, about 15 minutes). Set chicken aside to cool. Cut into strips.
Arrange lettuce on large serving platter. Toss with sliced chicken, avocado, grapefruit and onions. Drizzle with dressing before serving.
Enjoy a homemade salad dressing with every meal! Simply triple the ingredients for the Honey- Cilantro Vinaigrette, mix together as described above, then transfer to a small glass container or cup. This dressing can be stored in the refrigerator, covered, for up to 2 weeks. Let come to room temperature and whisk before using.