Looking at a map it seems like they would have at least tried, but I've never heard of any such occurrence. The only reason I can think of is maybe a shared Catholic religion would have stopped this.
First of all, Spain and Portugal formed part of the the same country under the "Union Ibérica" from 1578 to 1640 ruled by three different Spanish-born kings (easy to remember, they were all called Felipe II to IV).
Afterwards there were a few unsuccessful attempts (War of the Oranges, Ivansion of 1762) by Spain to invade the country, being the most famous of them when Spain allied itself with Napoleon allowing the French army to cross the country just to find itself occupied by their supposed French allies. This eventually led to the start of the Peninsular War.
In more modern times, General Franco also presented the Third Reich with plans to invade Portugal as to prevent a future British invasion of Europe that would naturally start from the land of their longtime allies. Not much really came out of this, as the Spanish army was in no state to take part in any wars due to the Civil War and the Germans had more pressing matters to attend.
Sources:
Breve Historia de España by José Manuel González Vesga Franco y Hitler by Stanley G. Payne