Bring a large pot of generously salted water to a rolling boil. Add the green beans and cook 2–3 minutes, until bright green and crisp-tender. Lift them out with a slotted spoon into a bowl of ice water to stop the cooking, then drain very well and pat dry. (Wet beans steam instead of sear.)

Pat the shrimp completely dry with paper towels — dry shrimp sear instead of steam. Season with 1/2 teaspoon of the salt and the black pepper.

Melt 2 tablespoons of the butter in a large skillet over medium-high heat until foaming. Add the shrimp in a single layer (work in two batches if needed) and sear 1 1/2–2 minutes per side, until pink, opaque, and lightly golden at the edges. Transfer to a plate.

Reduce the heat to medium. Add the remaining 3 tablespoons butter to the skillet. When melted, add the garlic and red pepper flakes (if using) and cook 30–60 seconds, stirring constantly, until fragrant and just turning golden — not brown.

Add the drained green beans to the skillet and toss to coat in the garlic butter. Cook 3–4 minutes, tossing occasionally, until heated through and glistening. Squeeze the lemon juice over the beans and toss again.

Return the shrimp (and any juices on the plate) to the skillet and toss 1 minute, just to rewarm and coat everything in garlic butter. Shower with parsley and serve immediately with lemon wedges.