How do you present the Gospel to followers of islam? Here is a video of a presentation that occurred in Dubai and it involved Thabiti Anyabwile and Bassam Zawadi in a discussion. This is the part by Thabiti and it confronts the problem of sin before a Holy God and provides the true solution to man's problem. It is not by works, but through the grace of God. Ephesians 2:8-9.
The way in which he presents the information helps to understand how forgiveness can be possible. Note how he clearly describes sin and the need for a Savior.