Melt 2 tablespoons butter in a large skillet over medium heat. Add bell peppers, shallot, and green onion; season with salt and pepper. Sauté until vegetables are soft, about 5 minutes.

Add corn, zucchini, water, and 2 teaspoons Cajun seasoning to the skillet. Cook until zucchini is tender, about 2 minutes. Stir in half-and-half and turn off the heat.

Meanwhile, season shrimp with remaining 2 teaspoons Cajun seasoning.

Melt remaining 2 tablespoons butter in a separate skillet. Add shrimp and cook in four batches until curled, pink, and cooked all the way through, 2 to 4 minutes per batch; do not overcook.

Divide corn mixture between four plates. Top each plate with 5 cooked shrimp. Serve immediately.