In a container with lid, mix together vinegar, oil, salt, pepper, and garlic. Once combined place chicken in marinade and mix until chicken is well coated.

Cover and place in refrigerator for at least 2 hours.

Turn grill to 500 degrees. Once grill reaches temp, reduce to 450 and place chicken directly on grill. Grill for 3-4 minutes per side, or until cooked through

Place onion in a food processor and process for 1-2 minutes. Onion will be almost a thick liquid consistency.

In a large sauce pan over medium-high heat, melt butter. Then add onion and stir for 2-3 minutes, or until onion begins to brown.

Add couscous, chicken broth, salt, and pepper. Stir well. Once liquid comes to a boil, cover and remove from heat. Let sit for 10 minutes.

Fluff couscous with a fork and stir in basil and tomatoes.

Cut chicken into thin slices and serve over couscous.