1. It's really simple. / It's very easy.
2. It's a piece of cake.
3. It's easy as pie. / It's easy as ABC.
4. It's no big deal!
5. It's a no-brainer!
6. I can do it with my eyes closed!
7. That's no sweat at all!
8. Nothing to it!
9. It's a joke. Anyone can do it.
10. It's a cinch!