Heat oven to 375°F. Spray large cookie sheet with cooking spray.
In medium bowl, place feta cheese; break apart large pieces with fork. Add spinach, onions, lemon peel, salt and pepper; mix well.
Separate dough into 8 biscuits. Separate each biscuit into 2 layers. Press or roll each to form 3 1/2-inch round. Place about 2 tablespoons spinach mixture on center of each round. Fold dough over filling, pressing firmly to compress filling; firmly press edges of dough with fork to seal. Place on cookie sheet.
Bake 12 to 16 minutes or until golden brown. Cool 5 minutes. Serve warm with cucumber-yogurt sauce.