In a bowl blend milk, cream of mushroom soup and eggs until smooth. Set aside.
Heat oil in a pan and saute onions until transparent. Add tuna flakes and saute about 5 minutes.
Take the chilled crust and grate 1/4 of the cheese bar over it.
Spoon the tuna over the cheese; dot with pimientos. Grate remaining cheese on top. Season with paprika.
Bake for 45 minutes or until toothpick inserted in the center comes out clean. Let stand at least 10 minutes before slicing.