Re-create a flowing curve

I am trying to create a flowing color band like the example below. I can’t seem to find the tools to reshape a circle or tutorial on how to draw lines that curve and then fill them. again, see the example below.


This looks like something that can be done with a handful of bezier paths (aka, the “pen tool”)

If you’re not too familiar with the tool, it might take a little bit of time to get to understand it - but once you get it, you should be able to knock this out in ~10 minutes.