Preheat a grill or grill pan.
Season chicken breasts on both sides with salt and pepper and drizzle with olive oil. Grill for about 4 to 5 minutes on each side or until cooked through. Set aside to rest for 2 minutes and then cut into bite-size pieces.
In a skillet, cook the prosciutto over moderate heat until it is crisp; transfer with a slotted spoon to paper towels to drain. Break into bite-size pieces.
Halve, pit, peel and cut the avocado into 1/2-inch pieces.
In a large salad bowl, toss together the romaine, corn, and watercress. Add the chicken, prosciutto, tomatoes, egg yolks and whites, and avocado.
Pour Grilled Onion Blue Cheese Dressing over salad and toss well. Divide over tortillas and fold or roll up to make a sandwich wrap.
Preheat a grill or grill pan. Onions can be grilled utilizing a stove top grill pan or outside grill.
Remove outer skin of the onion. Cut into 1/2-inch thick circles. Place in bowl and season with extra-virgin olive oil, salt, and pepper, to taste. Transfer onion to grill or grill pan and cook over medium-high heat until they have a transparent, caramelized color, about 5 to 7 minutes. Remove from heat and allow to cool, then cut into medium dice.
In mixing bowl, combine mayonnaise, sour cream, buttermilk, hot sauce, and Worcestershire until well blended. Add blue cheese and mix well to incorporate throughout dressing. Fold in diced grilled onions. Check for seasoning. Refrigerate until ready to use.