Place the chicken breasts in a small glass dish. Combine the lemon juice, olive oil, garlic, and red pepper flakes, and thyme leaves in a small bowl and pour over the chicken breasts. Let marinate at room temperature while preparing the couscous salad.
Heat 1 tablespoon olive oil in a medium saucepan over medium high heat. Add the couscous and, stirring constantly, cook for 4 minutes or until lightly toasted. Add the water and bring to a boil. Reduce the heat and simmer for 15 minutes or until the water is evaporated. Let sit for five minutes. Transfer to a bowl and place in the refrigerator to cool for 10-15 minutes while prepping the rest of the ingredients.
Meanwhile, combine the tomatoes, cucumbers, red onion, feta, olives, and parsley in a large bowl. Add the cooled couscous and toss to combine. Whisk the vinegar and olive oil in a bowl until combined; pour over the couscous salad and toss to combine. Season with salt and pepper to taste.
Heat a grill pan or grill. Remove the chicken breasts from the marinade and season with salt and pepper. Grill over medium-high heat for about 5 minutes per side, or until the internal temperature reaches 165 degrees. Let sit for 5 minutes and then slice on the diagonal. Serve alongside the couscous salad.
VEGAN OPTION: Eliminate the chicken and the feta and you have a delicious vegan main dish or side salad. Throw in some toasted pine nuts for added flavor.