Dying Light BBQ Trophy / Achievement will give you one Bronze trophy or 10 gamerscore points. To get this Trophy / Achievement you must burn a zombie by sticking it up on a spike. Do not kill it though.
For getting the Dying Light BBQ Trophy / Achievement, you will need three things, Spikes, Firecrackers and Molotovs. Spikes are very easy to find as they are peppered across the map. Look for them on streets, buildings, roadbloaks etc...
Save up some Molotovs and Firecrackers in your inventory. When you find a spike, release the firecrackers in such a way that it sets the spikes on fire and wait for the zombies.
When they reach the burning spike, throw a Molotov and then immediately kick them into the it. You do not want them to burn to death, so don't let them burn for too long.
If you are still not sure, watch the following video on how to get the Dying Light BBQ Trophy / Achievement. This game is now available on PC, PS4 and Xbox One.