Heat the oil in a large skillet over medium-high heat. Add the flour and cook, stirring often, until the roux is pale brown, about 10 min­utes. Add the onion, celery, and bell pepper. Cook until the onion is soft and translucent, 3 to 5 minutes. Add the garlic and cook until fra­grant, 45 to 60 seconds. 

In small bowl, combine the tomato paste and stock. Add the stock mixture to the skillet and bring to a boil, stirring constantly. Decrease the heat to medium and simmer until slightly thickened and the fla­vors have married, about 10 minutes. 

Add the shrimp, parsley, smoked paprika, and cayenne pepper. Cook until heated through, about 5 minutes. Taste and adjust for seasoning with salt and pepper. Spoon over hot rice, garnish with green onions, and serve immediately.