Heat a large nonstick ovenproof skillet over medium-high heat.
Add spinach to pan; cook 1 minute or until spinach wilts, tossing constantly.
Place spinach in a colander; press until barely moist. Wipe pan clean.
Combine spinach, cheese, nuts, thyme, juice, and garlic.
Cut a horizontal slit through the thickest portion of each chicken breast half to form a pocket. Stuff 3 tablespoons filling into each pocket. Seal with wooden picks.
Sprinkle chicken with salt and pepper.
Heat oil in pan over medium-high heat.
Add chicken; cook 3 minutes on each side or until brown.