1Cook penne to desired doneness as directed on package. Drain; cover to keep warm.
2Meanwhile, heat oil in large nonstick skillet over medium-high heat until hot. Add onions; cook 3 to 4 minutes or until softened, stirring frequently. Add garlic; stir to combine.
3Add tuna; cook 2 to 3 minutes or until browned on all sides. Add tomatoes, tomato sauce, capers and pepper flakes; cook about 1 minute or until mixture comes to a simmer. Reduce heat to low; cover and cook 1 to 2 minutes or until fish flakes easily with fork.
4Place cooked penne on serving platter. Top with tuna mixture. Sprinkle lightly with cheese.