Yes! You can start in Valenca do Minhon in Portugal and walk across the bridge /border into Tui, Spain. Then it's pretty much straight up to Santiago (Valenca, Tui, Porino, Redondela, Pontevedra, Caldas, Padron, Santiago). It's 115 km. Otherwise you can start in Tui. There is a book here for sale on the Portuguese Camino. Buen Camino/Ultreia
Ronces-SdC (03-04/10);Oporto-SdC (10/2011); VdlP via Portugal 03/04 2012/2013;Part Invierno 2012; Toulouse to Sarrance 2012; Ingles to Muxia June 2013 Cami Catala and Aragones 2014; El Salvador & Primitivo 2014; Camino de Madrid 2016; Levante 2015,2017
Actually there are several routes in Portugal and the route that they describe as 'central' goes up the middle of Portugal and through Chaves to Verin then joins one of the Sanabres variants, either the low route to Allariz or up to Laza. I did Chaves to Verin and up to Laza and didn't see a soul until Ourense but it would be different in summer. On the other hand for that central route the last 100k would be from Ourense!
Last year in September coming in to Santiago on the Portuguese route was very quiet. It did not even compare to the previous year coming in to Santiago on the Francés. The walk in to the city was nicer and shorter too.