1. Heat oven to 425°F Grease a small baking sheet.
2. Combine tuna, cheese, mayonnaise, parsley, lemon juice, onion, salt, and pepper. Blend thoroughly and set aside. (Note: You can use Swiss or another kind of cheese if you like.).
3. Add water to biscuit mix, and knead 10 times on a lightly floured surface.
4. Pat dough into a 10x12-inch rectangle in the center of the baking sheet.
5. Spread tuna mixture evenly down the center of the rectangle.
6. Make 6-7 cuts down each side of the rectangle, from the outer edge to the tuna mixture.
7. Bring the opposite strips up and over the filling and seal the ends to form a braid.
8. Sprinkle with celery seed.
9. Bake 15-20 minutes at 425°F.
10. Use two large pancake turners to lift onto serving plate.
11. Cut into pieces crosswise.