Heat oven to 375°F. Spray 2-quart casserole (about 9 inches in diameter) with nonstick cooking spray.
In medium saucepan, combine pasta sauce, milk, tuna, spinach, water chestnuts, 1/2 cup Parmesan cheese and carrot; mix well. Cook over medium-high heat until bubbly, stirring frequently. Spoon into sprayed casserole.
Separate dough into 10 biscuits. Top hot tuna mixture with biscuits. Sprinkle with 1 tablespoon Parmesan cheese.
Bake at 375°F. for 20 to 30 minutes or until tuna mixture is bubbly and biscuits are deep golden brown.