In a small bowl, combine tomatoes, basil and vinegar.
Cook fettuccine noodles according to package directions and drain.
Melt roasted garlic & herb butter in large skillet over medium heat. Add onions and cook until limp (about 5 minutes). Add chicken slices and cook until lightly brown (about 4 to 5 minutes per side).
Divide cooked noodles between individual serving plates. Add chicken slices, and then pour seasoned butter remaining in the cooking pan over the chick slices. Top with tomato-basil mixture.