Preheat the oven to 180 °C.
Halve the focaccia horizontally and place the two halves on a large baking tray, cut side facing up.
Spread the pasta sauce over both halves and sprinkle with three quarters of the cheese.
Arrange the tomatoes, tuna and asparagus on top, followed by the remaining cheese.
Season with salt and pepper.
Bake for eight to 10 minutes or until the cheese has melted.
Sprinkle with chopped parsley and serve immediately.
For a more economical variation, omit the asparagus.