In a small saucepan, combine 1/2 cup of the balsamic vinegar and 1 tablespoon of honey. Gently simmer over medium-low heat, stirring occasionally, until thickened and reduced by about half, about 15 minutes.

Remove from the heat and set aside.

While the balsamic reduces, pound chicken breasts to an even 1/2 inch thickness. Season both sides with 3/4 teaspoon salt and 1/4 teaspoon black pepper.

In a large skillet, heat 1 tablespoon of olive oil over medium-high heat. Add chicken and cook for 4 minutes per side until browned and cooked through.

Remove chicken and set aside. Reduce heat to medium and add remaining oil. Sauté red onion until softened, about 3 minutes.

Add garlic to the pan and sauté for 30 seconds until fragrant.

Add tomatoes, thyme, remaining balsamic vinegar, honey, salt, and pepper. Cook until tomatoes soften, about 2 minutes.

Return chicken to skillet, nestling into the tomatoes, and top with mozzarella pearls. Cover and cook for 1-2 minutes until cheese melts.

Uncover, drizzle with balsamic reduction, sprinkle basil, and serve warm.