Place first 4 ingredients in the bowl of a food processor, and process until coarsely chopped. Place spinach mixture in a bowl; stir in yogurt, 1/8 teaspoon salt, and black pepper.
Combine remaining 1/4 teaspoon salt, juice, and next 5 ingredients (through red pepper) in a medium bowl. Add chicken; toss.
Spread 2 tablespoons spinach mixture in each pita half. Divide chicken mixture among pita halves; sprinkle with bell pepper and nuts.
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