Heat ΒΌ cup olive oil in a large oven safe skillet over medium heat.
Add onions and stir to coat with oil. Sprinkle with a pinch of salt.
Cook onions, stirring occasionally to avoid burning until onions are tender and slightly caramelized, about 20 minutes.
Stir in balsamic vinegar and cook for another 1-2 minutes.
Place cooked onions in a small dish and set aside.
Return skillet to stove over medium heat and add remaining olive oil.
Season chicken with salt, pepper and thyme.
Add chicken and cook until all sides are brown and cooked thoroughly. Remove chicken from skillet.
Increase temperature to high. Add in beef broth and deglaze skillet.
Reduce temperature back to medium. Gradually whisk in flour until broth is thicken. Season with a pinch of salt, pepper and thyme.
Stir in cooked chicken and onions until combined with beef gravy.
Sprinkle with Swiss cheese and place in a 350 degree oven for about 10 minutes until cheese in melted and bubbly. Sprinkle with a pinch of thyme if desired.
To serve, place a few baguette slices in a shallow bowl. Top with chicken and gravy. Serve warm.