In the first Council of Ephesus, not the "Robber Synod" that it's often confused with, the Church at large agreed upon St. Cyril of Alexandria's Christology of "the one incarnate nature of God the Word."
Since that time, Oriental Orthodox Christians have held to the traditional Christological definition that Christ is true God and true man, fully divine and fully human, in one divine-human nature; the two being united without separation, without confusion, and without alteration.
Having said that, what theological necessity was there for a new Christology? It's easy for Eastern Orthodox Christians to accuse us of being "Monophysite" because strawmen, after all, are always more easily built than a defense of your own position.
Please don't claim that since your fathers accepted it, Chalcedon must have been right. Anyone who's taken a course in logic will tell you that truth isn't determined by majority vote. Even the doctrines of an Ecumenical Council must be demonstrably true, otherwise the council isn't ecumenical. For example, the First Council of Nicaea didn't accept that Jesus is co-equal and co-substantial with His Father for the fun of it, but because it can be demonstrated by Scripture.
If you are able to explain why the Chalcedonian Confession was necessary to supplant the Ephesian Christology, please do so as civilly and clearly as possible. I do not doubt that the Chalcedonian Confession, properly interpreted, is a legimimately Orthodox Christology, but I wonder if it was really worth dividing the Church over when the Cyrillian Christology was already sufficient.
If no one is able to clearly and fairly defend Chalcedon, please refrain from ever again claiming that Oriental Orthodox Christians are somehow "not Orthodox." We don't doubt your Orthodoxy, so please afford us the same kindness.
Grace and peace.