I invented this on the heels of the cheese variety. Most of my family actually like it better, though I'm partial to the cheese version myself. It's suitable as finger food, because it sticks together when cut unlike some other fish pies.
If you don't want to eat dairy with your fish --for instance because you're Orthodox and fasting-- leave out the eggs and crème fraîche and brush the top very liberally with oil before baking.
Thaw the phyllo pastry.
Drain the tuna and flake it into a bowl. Add capers, finely chopped onion and pepper, and season to taste with salt, pepper and paprika.
Use a largish, medium-deep, preferably rectangular dish. Brush it with oil. Line the bottom with 3 sheets of phyllo pastry, crumpled up a bit and slightly overlapping. Brush them with oil. Lay another sheet over it, flat, and brush that with oil too. Place another 2 sheets on top, crumpled to cover the whole surface.
Spread half the filling over the pastry. Cover with a flat sheet of pastry; brush with oil.
Layer 3 crumpled sheets, 1 flat sheet and 2 crumpled sheets on top, brushing with oil after every step.
Repeat with the rest of the filling and the rest of the pastry, ending with 1 or 2 flat sheets to cover the whole surface. Your dish should now be almost full.
Beat the eggs with crème fraîche and a little salt and pepper. Pour the egg mixture over the pastry, taking care that everything is covered (spread with a spoon or your hands if necessary).
Bake about 40 minutes in a medium-hot oven (180°C) until it's golden brown and sizzling. If you're not using eggs, take care that the top doesn't burn; cover with greaseproof paper halfway through to prevent this.