Dredge the fish in the flour. Meanwhile, heat the oil in a large skillet over medium heat until it shimmers. Add the fish and brown about 3 minutes on each side. Carefully lift the fish out of the skillet and set it aside on a platter; sprinkle with the salt and pepper.
Add the tomatoes, beans, and garlic to the skillet and bring to a boil over high heat. Cook 3 minutes. Reduce heat to low and return the fish to the pan along with the tarragon. Cover and cook 5 minutes or until the fish flakes when tested with a fork or the tip of a knife.