You can replace the surround with anything that is non-combustible such as tile, brick, marble, stone, etc. Probably this least expensive and least disruptive thing you could do is to paint the cast iron surround a different color. (I assume it's cast iron -- maybe it's powder coated sheet metal made to look like cast iron.)

If you decide to paint the existing surround, you obviously have to make sure you use paint that is compatible with the high heat environment of the surround.

If you want to install a mantile that surrounds the existing iron surround to sort of "dress it up", you could do that and then you would have a more traditional looking fireplace. That additional surround MIGHT be combustible like wood IF the specs for the insert show that you have enough clearance. If you need a little more clearance, you can install tile over the brick as a surround around the existing metal surround and then put in the wood mantle around that. If you did that, your fireplace would look similar to ours, although our gas insert is from a different manufacturer. How do you like yours, by the way, does it give nice cozy heat?