Preheat oven to 450 degrees.
In a medium sized bowl, mix the drained, chopped and squeezed spinach, feta cheese, cream cheese, garlic, half of the salt and black pepper, until well combined.
Cut a pocket into each chicken breast. Insert the knife 2/3 of the way into the side of the thickest part of the chicken and slice towards the thinnest part, stopping before cutting through, making a pocket rather than a flap.
Separate the spinach and cheese mixture into 3 parts and roll them into thick logs. Stuff each log into the pocket. Season with remaining salt and pepper.
Heat the olive oil in an oven-proof pan over medium high heat; then, add the stuffed chicken, “top” side down cooking for five minutes. Remove from heat, turn each breast over and place pan in the pre-heated oven. Bake for 15 minutes. If chicken breasts are thick, cook for 2-3 minutes longer or until juices run clear.