Preheat Grill To Medium Heat. Grill Sandwich Patties About 3 Minutes Per Side, Or To An Internal Temperature Of 160 Degrees F. Heat Oil In A Large Skillet Over Medium-High Heat. Saute Peppers, Onions And Garlic In Oil Until Softened. Place Patties In Pita Half With Peppers And Onions. Add Lettuce And Mustard If Desired.