Bring chicken broth and salt to a boil in a large saucepan; add grits, stirring with a whisk. Cover, reduce heat, and simmer 30 minutes or until liquid is absorbed, stirring occasionally. Remove from heat. Add 1/2 cup cheddar cheese, stirring until cheese melts.
Preheat oven to 375°.
Heat oil and butter in a large nonstick skillet over medium-high heat. Add onions, bell pepper, garlic, and mushrooms to pan; sauté 5 minutes. Sprinkle shrimp with black pepper, and add to pan; cook 1 minute. Stir in rind, juice, Worcestershire, and hot pepper sauce; cook 2 minutes. Remove from heat; cool slightly. Place grits and shrimp mixture in a large bowl; stir gently. Beat egg whites with a mixer at high speed until stiff peaks form. Gently fold egg whites into shrimp mixture. Spoon mixture into a 13 x 9-inch baking dish coated with cooking spray. Sprinkle with remaining 1/4 cup cheese. Bake at 375° for 25 minutes or until puffed and lightly browned. Let stand 20 minutes before serving.