First off, think about your own interests and try to match that. If the topic is meaningful to you, it will be easy for you to learn whatever you have to say. It’s only natural that your mind focuses better on topics you like.

If you like films, you could discuss the achievements of famous Spanish-speaking directors/actors. Do these names seem familiar?
Pedro Almodóvar
http://es.wikipedia.org/wiki/Pedro_Almodovar
El laberinto del fauno (Pan’s labyrinth)
http://es.wikipedia.org/wiki/El_laberinto_del_fauno

Music?
http://en.wikipedia.org/wiki/Gustavo_Santaolalla#Filmography

What are your interests big genius?

"would you like a burrito"
"what’s in it"
"x,y, and z"
"is that a traditional spanish food"

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