For the couscous: In saucepan over medium heat add olive oil, when hot, add the garlic and red pepper flakes. Add the sun-dried tomatoes and saute a few minutes more. Add olives and chicken stock and bring to a boil. Add the box of couscous, turn off heat and let stand covered for 5 minutes. Fluff with fork, and season with salt and pepper. Spread 2 cups on large plate, add in 1/2 pound feta, and let cool. Keep the remaining hot to serve with chicken. (Put in covered casserole and reheat in oven last 10 minutes with chicken.)
For the chicken: Preheat oven to 400 degrees F.
Trim chicken with a boning knife, if needed. Start at top of breast and carefully make a lengthwise cut from top to bottom and making a pocket about 2 inches, making sure not to pierce the other side of the breast. When couscous is cool enough to handle, carefully spoon couscous mixture into pocket. Even out the stuffing by gently moving it around with your hands. Wipe off any excess couscous from outside of breasts and season with salt and pepper.
Heat olive oil and butter in saute pan and brown off both sides of chicken. Place chicken on baking sheet and place in oven for 20 minutes.
While chicken is baking, make the sauce.
For the sauce: In saute pan that you cooked chicken breasts in, heat and add garlic. Deglaze with white wine and add lemon juice. Reduce by one third. Add in sun-dried tomatoes, let reduce for 2 to 3 minutes, add the olives, turn off heat, add the butter and stir to combine.
To serve, place couscous from oven on plate, cut chicken breast in half, top with sauce, crumble remaining feta cheese over.