Metaphysically, there is clearly no incompatibility between the divine unicity of God, on the one hand, as this is expressed in the Islamic shahadah, and the divinity of Jesus Christ, on the other hand, as this is expressed in the Nicene Creed. The Christian is not obliged to assume that Christ is on the same “level” as His Father; on the contrary the Father, who is the fons et origo of the Trinity, is “greater than I” (John 14:28), and it is from Him that the Son and the Spirit both derive their Divinity. The difference is that between the Absolute and the Relative Absolute.
Operatively, “He who has seen me has seen the Father” (John 14:9), and this is because the human form of Christ, the man Jesus of Nazareth, is precisely the form of the uncreated Logos, who in turn possesses precisely the same Divinity as does God the Father, with whom He is thus “consubstantial” (homoousion). Now since the Name is the Named, the Name IESUS is sacramentally and methodically none other than God; indeed this Name is “as much” God Himself as is the Name ALLAH.
It is true, of course, that the Name ALLAH is in a sense “more direct” than the Name IESUS, but this is simply because Islam is a religion of doctrinal Truth whereas Christianity is a religion of avataric Presence. Nonetheless every Divine Name qua form is other than the Divinity itself, even though qua essence it is that Divinity. ALLAH is and is not God, and in the same way IESUS is and is not God. Believing in the Divinity of Jesus Christ is essential for someone who uses the Jesus Prayer or another Christian formula, but—as I hope you can see—believing in His Divinity is in no way in conflict with believing in the Divinity of the One God.