Pat chicken thigh dry and season with salt and pepper.
Heat olive oil in a skillet over medium-high heat. Dice pancetta into 1/4-inch pieces, then add to the pan. Cook 5 minutes, until browned. Transfer to a plate lined with paper towels.
Add chicken thigh to the oil in the empty skillet. Cook 3 minutes on one side, then turn and cook another 3 minutes, until browned but not yet cooked through. Transfer to a plate. Pour off most of the oil in the pan.
Add garlic, anchovy and red pepper flakes. Cook 1 minute, then add diced tomatoes and basil. Cook 15 minutes, occasionally breaking up the anchovy and tomatoes as the sauce reduces.
Meanwhile, chop swiss chard leaves and stems into bite-sized pieces. When sauce is ready, stir in swiss chard, then nestle chicken thigh into the pan. Cover and cook 10 minutes more, or until chicken is no longer pink in the middle.
Divide chicken, chard and sauce onto plates. Top with crispy pancetta and goat cheese if desired.