Pat the shrimp dry. Moisture is the enemy of a good sear.
Use paper towels to blot the shrimp well.
Mix the Cajun seasoning. In a small bowl, combine 1.5 teaspoons smoked paprika, 1/2 teaspoon cayenne (less for mild), 1 teaspoon onion powder, 1/2 teaspoon dried oregano, 1/2 teaspoon dried thyme, 1/2 teaspoon black pepper, and 3/4 teaspoon kosher salt. Add a tiny pinch of sugar if you like a balanced heat.
Toss shrimp with oil and spices. In a bowl, combine the shrimp with 1 tablespoon oil, the spice mix, and 1 minced garlic clove (or 1/2 teaspoon garlic powder). Mix until evenly coated.
Preheat your pan. Heat a large skillet over medium-high.
Once hot, add a light drizzle of oil.
Cook the shrimp fast. Place shrimp in a single layer. Cook 1.5–2 minutes per side, until they curl and turn opaque with a light char. Avoid overcrowding; cook in batches if needed.
Add citrus and finish. Turn off the heat.
Add a squeeze of lemon or lime and a little zest. Toss to coat. Taste and adjust salt or heat.
Garnish and serve. Top with chopped parsley or green onions.
Serve over cauliflower rice, in tacos, or on a salad.