This will not be easy! There are no direct trains or buses.
You best bet appears to be the bus service four times per day between Porto and La Coruna which take about five hours.
Then from La Coruna to Oviedo you get another bus (four or five per day) with the same company to Oviedo again taking about 5 hours.
Cost will be about +-€ 50 each way
You can find the web site here:
www.alsa.es
For the return to Lisbon you would have to either come back by the same route via Porto or route via MIRANDA DE EBRO.
There is a train from Oviedo that leaves at 19:34 and connects with the daily train from Paris to Lisbon leaving MIRANDA DE EBRO at 00:40 and arriving in Lisbon at 11.03.
For more information see www.renfe.es
