Pat the shrimp dry. Moisture is the enemy of good browning.
Blot the shrimp with paper towels, then season with salt, pepper, and a pinch of red pepper flakes if using.
Preheat your pan. Set a large skillet over medium-high heat and add 1 tablespoon olive oil. When it shimmers, add half the shrimp in a single layer.
Sear the shrimp fast. Cook 1 to 2 minutes per side until just pink and opaque. Do not overcook.
Transfer to a plate and repeat with the remaining shrimp, adding a touch more oil if needed.
Build the lemon butter sauce. Lower heat to medium. Add 4 tablespoons butter to the skillet. When melted, add the garlic and cook 30 seconds until fragrant (not brown).
Pour in the broth and scrape up any browned bits. Stir in lemon zest and juice. Simmer 1 minute to thicken slightly.
Return shrimp to the pan. Toss to coat in the sauce for 30 to 60 seconds.
Taste and adjust seasoning with salt, pepper, or more lemon.
Sauté the cauliflower rice. In a separate skillet, heat 1 tablespoon olive oil over medium heat. Add cauliflower rice with a pinch of salt and pepper. Cook 4 to 6 minutes, stirring occasionally, until tender but not mushy.
If using frozen, cook a bit longer to evaporate moisture.
Finish and combine. Stir chopped parsley into the shrimp. Spoon the shrimp and sauce over the cauliflower rice. Top with green onions and a light sprinkle of Parmesan if you like.
Serve immediately. Add lemon wedges on the side for extra brightness.