Took far too long to get this simple health slider. Think I’m going to have to make a shield just to create another slider 
If you want to do something similar, use the UI > Slider component, remove the handle sub-objects, disable navigation, set your colours on fill and background and finally set the width on the fill area and fill objects to 0 otherwise you’ll end up with a health bar that never completely fills or empties.
Credit to Tomer-Barkan on the Unity forums for the fill/empty fix and Liz_The_Wiz for patience in Discord.