Heat oil in a small nonstick skillet over medium-high heat. Add green onions, carrot, celery, gingerroot, and garlic; sauté 2 minutes or until tender.
Combine green onion mixture, rice, water chestnuts, soy sauce, and Szechwan sauce in a large bowl; stir well. Crumble chicken over green onion mixture, and stir just until blended.
Preheat oven to 350°. Pack mixture into an 8 x 4-inch loaf pan coated with cooking spray; sprinkle sesame seeds over top of loaf. Bake at 350° for 50 minutes or until meat loaf registers 160°. Let loaf stand in pan 10 minutes.
Remove loaf from pan; cut into 12 slices. Serve with Chinese hot mustard and sweet-and-sour sauce, if desired.
Sandwich suggestion: Serve leftover meat loaf slices on sandwich bread with Chinese hot mustard and very thinly sliced green cabbage.