No, not the green peel, I suspect that’s a bit too hard and unyielding to make into a sweet. Although saying that, I have seen many Chinese bloggers make candies out of all sorts, so you never know! It’s the white part in-between the green skin and the red flesh that can be pickled or candied.
In many Greek homes they will serve guests something called glykó, or ‘spoon sweet’. These can be anything from orange rinds, cherries, walnuts and figs through to tiny baby aubergines. They are all very sweet, so you only need one piece, and you get a glass of iced water alongside to cut the sweetness.
I had a watermelon which finally had a thick white rind.
I had lemon balm in the garden.
I peeled the watermelon. This is not easy.
I cubed the white rind in a haphazard fashion.
Cover the rind in water, add the juice of 2 lemons, and leave for about an hour, then drain.
Make a simple syrup.
1 cup of sugar
1 cup of water
Mix together in a large pan and warm until the sugar has dissolved.
Submerge your watermelon pieces in the sugar water, and continue to simmer until it’s syrupy.
Pop into sterilised jars, and add a piece of lemon balm to each jar. You only need a few leaves as it is quite strong.
Seal the jars by simmering them in boiling water for 10 minutes.
The water should cover the lids.
CAREFULLY remove them after 10 minutes and leave to cool completely.
I used jars with lids that ‘give’ a little when pressed.

When they no longer give, they are sealed. If they still have a bounce, try processing them again, though if you are going to eat this fairly soon, keep it in the fridge and live dangerously.
Ideally keep for at least a few weeks before opening so they mature. I forgot about mine so waited quite a few months!
DO NOT FORGET YOU ADDED LEMON BALM LIKE I DID because I panicked and thought it had gone mouldy and nearly threw a jar away.
Wonderful chopped finely and stirred into ice cream.