Heat a large skillet to medium high heat. Salt and pepper the chicken breast and set aside.
Once skillet is hot, add the oil. Toss in the apples and cook for 4-5 minutes, tossing occasionally, and remove once apples are soft and lightly browned. Set aside, keep the skillet hot.
Now toss in the pancetta. Cook until crispy, another 3-4 minutes. Set aside with the apples. Keep approximately 2 tablespoons of the pancetta fat in the pan, and return the skillet to the heat.
Now cook the chicken. Cook for 3-4 minutes per side. After 3 minutes, toss in the leeks and garlic around the chicken. Let them saute while the chicken is cooking, gently stirring to cook evenly.
Pour in the chicken broth. Scrape the bottom of the pan to flavor the broth with any brown bits from the leeks, garlic, and chicken. Reduce the heat to a simmer. Place apples and pancetta back to the pan. Cover the dish and cook another 5 minutes or until the chicken is cooked through, the sauce thickens, and the remaining ingredients heat up with the chicken.
To serve, salt and pepper to taste. Top with toasted pecans and fresh thyme. Be sure to spoon additional sauce on top of the chicken.