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, if desired.
Unbaked casserole may be made one day in advance. Cover and refrigerate. Let stand at room temperature 30 minutes before baking as directed. To freeze unbaked casserole, prepare as directed, omitting Parmesan cheese. Cover tightly, and freeze. Let stand at room temperature 30 minutes before baking. Bake, covered, at 350° for 50 minutes. Uncover; sprinkle evenly with Parmesan cheese, and bake 10 more minutes or until cheese is lightly browned.
*1 (10-ounce) package frozen onions and peppers may be substituted for fresh onion and bell peppers.
**1 (10 3/4-ounce) can cream of mushroom soup may be substituted for cream of shrimp soup.