Preheat oven to 180 C (350 F/Gas 4). Lightly spray holes of a 6-hole giant muffin tin with cooking spray.
Lightly spray 1 sheet filo pastry with cooking spray. Fold in half crosswise, then spray lightly. Fold in half crosswise again, then use to line a muffin hole, overlapping the pastry edges and pressing together to completely line the hole. Fold pointed edges of pastry back and tuck into the muffin hole. Repeat with remaining sheets of pastry.
Heat oil in a small saucepan over medium heat. Add onion and cook, stirring occasionally, 5 minutes, until soft. Add paprika and stir 30 seconds. Set aside to cool 10 minutes.
Whisky eggs in a bowl. Stir in onion mixture, tuna and parsley. Season with pepper and spoon into pastry in muffin holes. Sprinkle with cheese and bake 25 minutes, or until puffed and set in the centre.
Carefully lift tartlets out of muffin tin, transfer to individual plates and serve immediately.
You can used canned salmon instead of tuna if you prefer. The pastry is lovely and crisp after cooking but will soften if the tartlets are left to stand.