Since this word is made up of a single kanji, it should use the kun'yomi reading. You haven't learned this reading yet, so here's a mnemonic to help you:

You really want to eat food that's in neat shapes, so you decide to use a cutter (かた) on your cheese (ち) to make it a new shape. Square cheese is so boring. After you cut it up you have mouse shaped cheese! It just tastes better like that.