In a small saucepan, combine 0.5 cup of balsamic vinegar and 1 tablespoon of honey. Gently simmer over medium-low heat, stirring occasionally, until thickened and reduced by about half, approximately 15 minutes.

Remove from heat and set aside.

Prepare the chicken by pounding it to an even 0.5-inch thickness, season with 0.75 teaspoon salt and 0.25 teaspoon pepper on both sides.

Heat 1 tablespoon of olive oil in a large skillet over medium-high heat. Add chicken breasts and cook undisturbed for 4 minutes until lightly browned. Flip and cook another 3 minutes, checking for an internal temperature of 165°F.

If additional cooking time is needed, flip again and cook until done. Remove chicken and keep warm.

Reduce skillet heat to medium. Add remaining tablespoon of oil, cook diced red onion until softened, about 3 minutes. Add garlic and cook 30 seconds.

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

Return chicken to the pan, nestling into the tomatoes. Scatter mozzarella pearls over the top, cover, and cook for 1-2 minutes until cheese melts.

Remove from heat, drizzle with balsamic glaze, sprinkle with basil. Serve warm.