For the pitas: Heat olive oil in large skillet over medium-high heat. Add Jimmy Dean(R) Hearty Original Sausage Crumbles, oregano, and garlic and cook for 4 to 5 minutes or until sausage is hot, stirring frequently. Stir in lemon juice.
Combine spinach, tomatoes, cheese, olives, and pepper in large bowl.
For the tzatziki sauce: Mix the sour cream, cucumber, mint, lemon juice, and salt until well blended; cover. Refrigerate until ready to serve.
To assemble: Fill pita halves with sausage mixture, then spinach mixture. Add onion slices, if desired and drizzle with tzatziki sauce.