Pit and thinly slice olives. In a small bowl stir together olives, goat cheese, thyme, and salt and pepper to taste until combined well. Pat chicken dry and season with salt and pepper.
Put a chicken breast half on a cutting board and, beginning in middle of 1 side of breast half, horizontally insert a sharp thin knife three fourths of the way through center, moving knife in a fanning motion to create a pocket. Form pocket in remaining breast half in same manner. Divide filling between pockets and spread evenly with a finger.
Pat chicken dry and season with salt and pepper. In a small heavy ovenproof skillet heat oil over moderately high heat until hot but not smoking and brown chicken, skin sides down, about 2 minutes. Turn chicken over and brown about 2 minutes more. Transfer skillet to middle of oven and bake chicken until cooked through, about 15 minutes.
