For the spice blend: Whisk paprika, thyme, oregano, cayenne, garlic powder, onion powder, white pepper, and black pepper together in a small bowl.

For the étouffée: Drain shrimp in a colander for at least 15 minutes. Transfer to a bowl lined with paper towels and dry shrimp for about 3 minutes. Remove paper towels from the bowl. Season shrimp with salt and 1 teaspoon spice blend; toss to coat.

Heat oil in a large heavy skillet over high heat until oil is smoking. Cook shrimp in hot oil without stirring for 1 minute; stir, and cook 1 minute more.

Transfer shrimp to a large bowl. Let stand until juice collects in the bowl. Strain shrimp juices into chicken stock to total 2 cups, adding more chicken stock if necessary. Set aside.

Melt butter in the same skillet over medium heat until butter begins to turn tan at the edges. Sauté onion, bell pepper, and celery in hot butter until softened, about 5 minutes. Stir in remaining spice blend.

Sprinkle flour into vegetable mixture and sauté until combined, 3 to 4 minutes. Stir in tomatoes; cook until tomato juices begin to brown on the bottom of the pan, about 3 minutes. Whisk in chicken stock mixture, stirring until smooth. Bring to a simmer and cook until slightly thickened and reduced to a gravy consistency, 3 to 5 minutes. Stir in Worcestershire and hot sauce. Season with salt to taste.

Stir shrimp into étouffée sauce; let simmer until shrimp are cooked all the way through and no longer translucent, about 1 minute.

Garnish with green onions and a dusting of cayenne pepper. Pour over rice in large, shallow bowls.