Prep the shrimp: Pat the shrimp completely dry and season with the salt and pepper. Dry shrimp sear and pick up color; wet ones just steam.
Cook the asparagus: Heat the olive oil and 1 tablespoon of the butter in a large skillet over medium-high heat. Add the asparagus and cook for 3-4 minutes, stirring occasionally, until crisp-tender and bright green. Transfer to a plate.
Bloom the garlic: Reduce the heat to medium and melt the remaining 2 tablespoons butter in the same skillet. Add the garlic and red pepper flakes if using, and cook for 30 seconds until fragrant, stirring so the garlic doesn't burn.
Sear the shrimp: Add the shrimp in a single layer and cook for about 1-2 minutes per side, until they turn pink and opaque and curl into a loose C shape. Pull them off the heat right away; a tight O shape means they're overcooked.
Finish and serve: Return the asparagus to the skillet, squeeze in the juice of half the lemon, and toss everything together for 30 seconds to warm through. Sprinkle with parsley and serve with the lemon wedges on the side.
Notes
Cook the asparagus first and remove it, then sear the shrimp just until they turn pink and curl into a loose C, about 1-2 minutes per side. A tight O shape means the shrimp are overcooked, so pull them off the heat right away.