If you are talking about green-cheeked conures, then a cinnamint has the cinnamon gene and also is a dilute turquoise (mint). And an opamint would be a visual yellow-sided which is also dilute and turquoise. The dilute gene and the turquoise gene are both recessive. Since both parents are mints, all offspring would be dilute turquoise also. That part is easy.
However, both cinnamon and yellow-sided are sex-linked genes. Since you don't know which one is female, that complicates things a lot. Also, unless you know the male's full parentage, you can't know for sure if he could be split to other trait, which adds to the range of possible outcomes.
If your cinnamint is male and the opamint is female, and the male is NOT split to yellow-sided, then all girl offspring will be cinnamints. All boys will be normal mints, split to yellow-sided and cinnamon.
If he IS split to yellow-sided, then the results are more complex. Half of the female offspring will be cinnamint and the other half will be mooncheeks - dilute turquoise with both cinnamon and yellowsided visually expressed. Half the male offspring will be mint and the other half will be opamint.
On the other hand, if your opamint is male and the cinnamint is female, the results will be flipped. All girls will be opamints, like their dad. All boys will be mint, split to cinnamon and yellow-sided. If the male is split to cinnamon, you would have a chance to get mooncheek girls and cinnamint boys along with the expected results.