In a medium bowl, whisk together olive oil, honey, thyme, garlic, balsamic vinegar, salt, and pepper until well combined. Gently fold in fresh blueberries, being careful not to crush them too much. Some will break naturally during cooking to create the sauce.

Place chicken breasts in a large resealable bag or shallow dish. Pour marinade over chicken. Seal bag and massage gently to coat, or turn each piece in the bowl until fully covered. Refrigerate for at least 30 minutes, up to 2 hours for best flavor.

Preheat oven to 400°F (200°C). Heat a large 12-inch oven-safe skillet over medium-high heat with a drizzle of olive oil.

Remove chicken from marinade, reserving all marinade in the bowl. Sear chicken breasts for 3-4 minutes per side until golden brown and slightly caramelized.

Pour reserved marinade with blueberries over the seared chicken in the skillet. Transfer skillet to preheated oven.

Bake for 15-20 minutes until chicken reaches an internal temperature of 165°F (75°C). Insert meat thermometer into the thickest center portion of the breast to check.

Remove from oven and let chicken rest for 5 minutes before slicing. Spoon warm blueberry sauce over top and serve immediately.