There is actually an association for Leitão in Portugal and here is an in-depth list of restaurants that serve Leitão in Mealhada.
Even if you don't read Portuguese, the info and addresses should help. If you need any assistance translating, please let me know.
That website lists so many places that it just added to my inability to decide.
When I visited the area someone recommended Casa Vidal in Aguada de Cima. Off the beaten path (Mealhada), but once we found the place it was very good. And the pig was washed down with a nice sparkling red Bairrada - it does work well.
The restaurant recommended to us by "Chefe Silva", a famous Portuguese chef is:
Restaurante "A NOVA CASA DOS LEITÕES", Estrada Nac.1 - Peneireiro, 3780-623
Aguim. Tel.: 231 518025 Fax: 231 518027 Especialidades: Leitão à Bairrada, Chora do
Mar. Closed Mondays (?)
I understand it is just outside of Mealhada, North on the main road, but we have not been there yet. Traditionally, the Leitão is served with the local red bubbly, and strangely
enough it goes well with it (cuts the fat of the suckling pig). Have fun!