Spell the character's name correctly. Sometime before the point where the pronunciation becomes important, clarify it in the text, e.g. another character might mispronounce it and be corrected, or someone makes a point of the pronunciation in a conversation, or someone -- the narrator, if necessary -- can simply state that the name is pronounced the Spanish way.

Or else don't make a point of it, and trust your readers to catch on -- they probably will, if you've provided enough context/clues to allow them.