As Renfe (Spanish Rail) canceled all their Nighttrain Operations in this Pandemic and plan not to get them back in service.  There are only Routes with Several changes possible.

First way get a Connection to Vigo and then further via Porto to Lisbon.

Option B is to go to Badajoz and from there with CP Trains (Rail of Portugal) further to Lisbon

I can highly recommend the route via Vigo: the part Astorga - Vigo is very scenic and lets you see a different part of Spain (green and mountainous), and Vigo itself is a relaxed city. It seems that there have been emerging some hostels since the last time I was in Vigo. Stay overnight in Vigo, then take the 9am train to Porto (reservation needed, can be done online), then Porto IC to Lisbon.

While you're in Vigo and have some time, consider exploring some its surroundings, which are very beautiful, especially las Islas Cíes. It has one of the best beaches in the world, Praia das Rodas. Keep in mind that you're in the Atlantic Ocean here, so even in summer it could be 15 degrees. 

For the return journey (if you're going back by train), would be as described by seewulf via Badajoz. Stay overnight in Madrid, take the AVE to Barcelona or Girona, then regional train to Cerbère/Portbou, where the night train to Paris leaves.