Melt 1/4 cup butter in large skillet over medium-high heat. Add onion and next 3 ingredients; sauté 7 minutes or until tender. Add garlic, and sauté 1 minute. Stir in okra, lemon juice, and salt; sauté 5 minutes. Add shrimp, and cook 3 minutes or until shrimp turn pink. Stir in soup and next 4 ingredients until blended. Pour into a lightly greased 11- x 7-inch baking dish. Sprinkle evenly with Parmesan cheese.
Bake at 350° for 15 to 20 minutes or until casserole is bubbly and cheese is lightly browned. Garnish with fresh lemon slices and parsley.