In a small bowl combine feta cheese and cream cheese; set aside. Using a sharp knife, cut a horizontal slit through the thickest portion of each chicken breast half to form a pocket. Stuff pockets with the cheese mixture. If necessary, secure openings with wooden toothpicks. Sprinkle chicken with pepper and salt.
In a large nonstick skillet cook chicken in hot oil over medium-high heat about 12 minutes or until tender and no longer pink, turning once (reduce heat to medium if chicken browns too quickly). Remove chicken from skillet. Cover and keep warm.
Carefully add chicken broth to skillet. Bring to boiling; add half of the spinach. Cover and cook about 3 minutes or just until spinach is wilted. Remove spinach from skillet, reserving liquid in pan. Repeat with remaining spinach. Return all spinach to skillet. Stir in the nuts and lemon juice.
To serve, divide spinach mixture among 4 dinner plates. Top with chicken breasts. If desired, garnish with lemon slices.
Tip: If basil-and-tomato feta cheese is not available, stir 1 teaspoon finely snipped fresh basil and 1 teaspoon snipped oil-pack dried tomatoes, drained, into ¼ cup plain feta cheese.
To toast nuts, spread in a shallow baking pan lined with parchment paper. Bake in a 350°F oven for 5 to 10 minutes or until golden, shaking pan once or twice.