Many earnest Muslims think they already know Jesus because they know he is a prophet. To know Jesus as a prophet is to know him only in a small way, a partial way. One way to explain how Jesus is more than a prophet is to explain that he is the Qibla, the place where we expect to meet God when we direct our prayers. While the Muslims now pray towards Mecca, they once prayed towards Jerusalem towards the ruins of the Temple. The shrine in Mecca now holds the same place in their mind that Jerusalem's Temple holds for the Jews: they direct their prayers there. But Jesus said that the Temple would not be replaced by some other earthly place such as Mecca, but that he himself replaced the Temple. He is where we go to meet God, he is the direction towards which we pray, he is where we expect miracles and the presence of the Holy One. In the same way that Muslims are aware that bowing to Mecca to pray is not idolatry towards Mecca, in the same way Christians bowing and praying to God through Christ is not idolatry, but simply meeting God where he can be found.
Of course, Christ is far greater than that, but you have to start a conversation somewhere.