Hi Mango,
This effect was not achieved by using the lens flare in the post process.
This effect was essentially “cheated” by creating a particle effect with an emissive unlit material.
As you can see with these attached images (granted mine aren’t final or all that good. Just quickly thrown together for reference)
In this first image you’ll see the particle working in the scene.
Next is the particle system and viewing it in Cascade
And this is basically all you need for the texture.
When setting up the particle system there are a lot of features in here to tweak to get a good look. The basic look I have here I used the defaults and only got rid of the velocity to not have the lens flare move. There are some other things to change as well to get it perfect!
Have fun with it and if you have any questions let me know!