Step 1

Bring water to a boil in a stockpot over medium-high. Add shrimp; boil until opaque and just pink, about 2 minutes. Drain and rinse under cold water until cold, about 2 minutes. Pat dry with paper towels.

Step 2

Combine shrimp, okra, onion, peppers, and thyme sprigs in a large glass bowl or trifle dish.

Step 3

Whisk together oil, vinegar, salt, black pepper, and red pepper in a bowl until emulsified. Thinly slice 1 lemon; add slices to shrimp mixture. Juice remaining lemon to equal 1⁄4 cup; whisk juice into oil mixture. Pour dressing over shrimp mixture, stirring to combine. Cover and chill at least 8 hours, stirring occasionally. Stir in basil just before serving.