Heat the 1/2 cup of the oil in a Dutch oven or large, heavy pot over medium-high heat. Add the flour, reduce the heat to medium, and cook, stirring constantly with a large wooden spoon, to make a roux the color of peanut butter, about 15 minutes. Add the onions, bell peppers, and celery, and cook, stirring, for 1 minute. Add the garlic and bay leaves, and cook, stirring, for 30 seconds. Place the tomato paste in a small bowl and whisk in the sherry to blend. Add to the pot, and cook, stirring, for 30 seconds. Add the stock, whisking to blend. Add the tomatoes and their juices, the sugar, salt, black pepper, and red pepper flakes, and cook, stirring, occasionally, for 20 to 25 minutes.
Reduce the heat to low then whisk in the butter, bit by bit, until incorporated. Remove from the heat, taste, and adjust seasoning, if necessary. Preheat a grill to medium. To grill the fish, brush the fish all over with the olive oil and season the fish with the Essence. Grill the fish, basting occasionally with additional olive oil for about 8 minutes. Turn the fish and grill briefly on the second side. Return the court bouillon to the heat, add the fish, and simmer until just cooked through, about 3 to 4 minutes longer. To serve, spoon 1/2 cup of rice into the center of six large soup bowls and divide the red fish court bouillon equally among them. Serve immediately, garnished with parsley or green onion.