1. Poach shrimp: In a medium pot, combine 6 cups water, Old Bay, and lemon; bring to a boil. Add shrimp and simmer until opaque throughout, 2 to 3 minutes. Drain, discard lemon, and transfer shrimp to a bowl.

2. To serve: Toss shrimp with vinegar, mustard, and 2 tablespoons oil. In a large skillet, heat remaining 2 tablespoons oil over medium-high. Add green beans and cook until bright green, 4 minutes. Add corn and zucchini; saute until crisp-tender, 5 minutes. Transfer to a platter. Top with shrimp mixture, season with salt and pepper, and serve warm.