In a large skillet with a lid, melt 2 tablespoons butter over medium. Add white part of scallions, lemon zest, broccoli, and 1/2 cup water; season with salt and pepper, and toss. Cover, and cook until broccoli is bright green and just beginning to soften, 3 to 4 minutes.
Add shrimp and peas. Cover, and cook, tossing occasionally, until shrimp are opaque and peas are tender, 4 to 6 minutes.
Add lemon juice, green part of scallions, and remaining butter; season with salt and pepper. Toss gently and serve.