Prepare the ingredients by dicing the chicken breast into bite-sized pieces and halving the Brussels sprouts.
In a large skillet over medium heat, add the pancetta and cook until crispy and the fat has rendered. Remove the pancetta with a slotted spoon and set aside, leaving the fat in the pan.
Add the olive oil to the skillet with the pancetta fat. Season the chicken pieces with sea salt and black pepper, then add them to the pan. Sear until golden brown and cooked through, about 5-7 minutes.
Move the chicken to one side of the pan and add the Brussels sprouts, cut-side down. Let them sear undisturbed for 3-4 minutes until they develop a deep brown char.
Add the minced garlic to the pan and stir everything together, cooking for an additional 1 minute until fragrant.
Pour the balsamic vinegar over the mixture. Stir constantly as the vinegar bubbles and reduces into a thick, glossy glaze that coats the chicken and sprouts.
Fold the crispy pancetta back into the skillet, toss once more to combine, and serve immediately while hot.