Combine the chicken breast with olive oil, salt, and pepper in a bowl. Marinade for 30 minutes.
Preheat grill to medium high heat.
Grill each side of the chicken breast for 7-8 minutes. Allow the chicken to cool to room temperature.
For the sauce, combine the Greek yoghurt and sriracha sauce. Spread on each slice of bread.
For each sandwich, add 3 oz (1 quantity) chicken, 1 slice Swiss cheese, 1 romaine lettuce, and 2 tomato slices.
This is an excellent lunch. For a healthy plate, pair up this sandwich with the Salad with Cilantro Lime Dressing. To achieve 2-3 CHO servings, end your meal with 2 cups of strawberries.