In a large saucepan cook the pasta in lightly salted boiling water for 4 minutes; drain and set aside. (Pasta will not be tender.)
Meanwhile, sprinkle both sides of the fish steaks with the Creole seasoning; set aside. (If using a salt-free Creole seasoning, sprinkle fish with 1/4 teaspoon salt.) In a medium bowl combine the partially cooked pasta, mushrooms, wine, pesto, lemon juice, and capers; set aside.
In a large skillet cook the fish steaks in the hot oil over medium-high heat for 1 minute; turn and cook 1 minute more. Reduce heat to medium. Spoon the pasta mixture around the tuna steaks in the skillet. Bring to boiling; reduce heat. Simmer, covered, over medium heat for 6 to 9 minutes or until fish flakes easily with a fork. Makes 2 servings.