How do you get the chain back on easily?

So I have a Tern GSD gen 1. When the chain comes off of the front/motorised cog - is there a way to easily get it back on? It's surrounded by a plastic casing so it normally involves 10 minutes of getting frustrated and swearing and getting really oily hands with a few cuts.

What about the newer gen 2 chain bikes? Are they easier to access the chain because they don't look it.

I know it's a sign I probably need to replace the chain.