Prepare barbecue (medium-high heat). Grill Pioneer sausages until cooked through, turning occasionally, about 10 minutes. Grill fully cooked sausages until heated through, about 7 minutes. Transfer sausages to platter. Cover to keep warm.
Arrange pita halves in 2 stacks and wrap in aluminum foil. Place foil packets on grill to warm pita, about 10 minutes.
Fill pita halves with lettuce. Place grilled sausage halves atop lettuce in each pita half; serve with mustard.