Pat chicken breasts dry with paper towels.
Season both sides generously with garlic salt and let rest at room temperature for 10 minutes.
Heat olive oil in a cast iron skillet over medium-high heat until shimmering.
Sear chicken breasts for 4-5 minutes on the first side until golden and crispy.
Flip and sear the other side for 4-5 minutes more until internal temperature reaches 165°F.
Remove chicken to a clean plate and tent loosely with foil to keep warm.
In the same skillet, reduce heat to medium and add minced garlic and diced red onion.
Sauté until the onion is translucent and fragrant, about 2-3 minutes.
Carefully add balsamic vinegar and honey, stirring to combine.
Simmer for 3-4 minutes, allowing the balsamic to reduce and thicken slightly.
Return the chicken to the skillet and nestle it into the sauce.
Top each chicken breast with a slice of fresh mozzarella.
Cover the skillet and cook for 3-5 minutes until the mozzarella is completely melted.
Arrange on serving plates and top with cherry tomatoes and fresh basil slices.
Drizzle any remaining sauce from the pan over each plate and serve immediately.
