Preheat the oven to 180°C (350°F).
Cook the penne pasta in a large pot of boiling salted water according to the package instructions until al dente. Drain and set aside.
In a large saucepan, heat the olive oil over medium heat. Add the chopped onion and cook for 5 minutes until softened.
Add the minced garlic and cook for 1 minute until fragrant.
Add the butter to the saucepan and let it melt. Stir in the plain flour and cook for 1-2 minutes to form a roux, stirring constantly.
Gradually whisk in the milk and double cream, continuing to stir until the sauce thickens, about 5 minutes.
Remove the sauce from heat and stir in half of the grated cheddar cheese until melted.
Add the canned chopped tomatoes, dried oregano, dried basil, salt, and black pepper to the sauce. Stir to combine.
Fold the drained pasta and flaked tuna into the sauce, mixing gently to combine.
Transfer the mixture into a 9×13 inch (23×33 cm) baking dish.
Sprinkle the remaining cheddar cheese and grated Parmesan evenly over the top.
If freezing for later, cover the baking dish tightly with foil and label with the date. Freeze for up to 3 months.
To cook immediately, bake uncovered in the preheated oven for 25-30 minutes until the top is golden and bubbling.
If cooking from frozen, bake covered with foil at 180°C (350°F) for 45 minutes, then remove foil and bake for an additional 15 minutes until golden and bubbling.