Hola...I think the trick is to choose something short, sweet and catchy. For example, "¡Comamos!" means "Let's eat!" It is very direct and to the point and simple for people to remember who may like the food but not know the language.
I have some other ideas but this was the first one that popped into my mind, and you know what they say about first impressions.
Is it presumptuous of me to think that all the "good" names have already been taken? (Ha!) One needs only to look around at the local Spanish restaurants in one's town to find some names (albeit some cheesy ones). First let me say that I really like the examples given by stolperia just because they truly encompass the Spanish language in a way that your teacher will appreciate. I wonder if you are supposed to put a particular flare on your restaurant? Is it supposed to be traditionally Spanish (as in from Spain)? Or is it supposed to have a more Cuban or more Mexican flare? If so you could call it something like "Espana en Los Estados Unidos," or insert the Spanish name for the desired country. You could also include the name of specific foods indicative of the region if you wanted. It might give it a bit more kick than our usual "Taco Casa" or worse, "Taco Bell." Ugh.
It might be helpful to narrow the range for your restaurant. You need for the name to be in Spanish, so the obvious choices would include names of Spanish foods that you have in your vocabulary. Beyond that, do you want to focus on a certain type of Spanish food? If so, that focus can give more direction to your search for a name for your restaurant.
Examples: If you want to feature seafood, you would want to include the word "mariscos" in your name. Add a descriptive word or phrase and you might have your restaurant name. "Magnifico Marisco" means "Magnificent Seafood" and has alliteration and a nice rhyme, which would help your potential customers remember the name! "Tacos de ir" means "Tacos To Go" if you decide your restaurant is going to specialize in tacos. "¡A Comer" means "Let's Eat" in Spanish. The upside-down exclamation point at the beginning of the name would be a visual cue to make the name more memorable.