Meatball Pita

• 24 meatballs
• 12 skillet with nonstick cooking spray
• 4 wheat pita breads (whole)
• 700 gr extra beef (lean ground)
• 240 ml nonfat yogurt (plain)
• 160 ml yogurt
• 160 gr tomato (chopped)
• 130 gr mushrooms (sliced)
• 45 gr shallots (finely chopped)
• 45 gr salt and pepper