1.Preheat barbecue to medium-high heat; place grilling basket on grill
2.Spread dijon mustard on top and bottom of the naan
3.Combine zucchini, red onion, oil, salt, and pepper in a bowl; stir well to coat. Transfer to grilling basket; cook, stirring often, for 4-5 minutes, or until golden and tender. Remove from heat; reduce barbecue to medium-low heat
4.Arrange cheese evenly over naan bottom; fold chicken on the cheese, place grilled vegetables, and cover with naan top
5.Carefully transfer sandwiches to grill; cover and cook for 2-3 minutes per side, or until cheese is melted and naan rounds have grill marks
6.Remove from heat and open sandwich; add tomatoes and arugula. Serve immediately