MONO is relative pronoun like WHAT in next sentence; WHAT I eat is UNAGI. In this case, main verb in the sentence is not EAT, but IS. TOKORO and HITO are often used like that too. Some examples... 私が住んでいる所は新宿駅の近くです。The place where I live is near the shinjuku station. 君が話しかけた人が私の母親です。The person who you talked to, is my mother. And you can choose ending form(口調Kucho) as you like. DESU(-MASU) form is polite, respectful way to speak. DA form sounds relatively rough, but preferred in written text, since it is short and clear.