Prepare the dough first. In a bowl, pour the yeast in water and mix until it dissolves. Set it aside. In another bowl, mix the flour and salt. Make a well in the middle and add the water and yeast mixture.
Mix the dough by hand until it reaches a homogenous texture, and then add the oil. Keep kneading the dough, until the oil is absorbed and the dough reaches a point where it does not stick in your hands.
Once the dough is ready, set it aside for one hour in a greased bowl covered by a clean cloth.
After one hour, the dough will have considerably increased in size, thanks to the yeast effect. Now you have to divide it in equal parts: one for the top and the other for the base.
Lay half of the dough over the table or countertop to knead it. Use a rolling pin until it has reached uniform thickness.
Grease and flour a baking tray. Lay the dough that was set aside for the base. With a fork, make some very tiny holes on the dough so that no air bubbles are formed with the heat.
Proceed with the filling: sauté the onion with the bell pepper and sweet paprika. Then, add the drained tuna and cook it slow and low.
Pour the filling over the pie base with a chopped hard-boiled egg. Cover the pie using the other portion of the dough. Fold the edges to seal it and make some tiny holes again on the dough with a fork, this time only on the top.
Brush the tuna pie top and bake it in preheated oven (356ºF) for 40 minutes.
Voilà, your Galician tuna pie is ready to eat.