Combine tuna, frozen peas, cheddar cheese, celery, bread crumbs, onion, and salt and pepper in a large bowl. Add mayonnaise; mix well. Spoon into 10x6 baking dish. Separate crescent roll dough into 2 rectangles; press perforations to seal. Cut dough into 4 long and 8 short strips. Place strips over casserole in lattice design. Brush lightly with mayonnaise. Sprinkle with sesame seeds. Bake at 350*, 35-40 minutes or until crust is golden brown. Serve with Cool Cucumber Sauce.
For Cool Cucumber Sauce: Combine mayonnaise, sour cream, cucumber, chives, parsley, salt, and dill weed. Mix well and chill.