Have you seen there is a topic about flavouring U/U Huel? Maybe you can find some useful info there 
I use U/U. The very first Huel-shake I made was with strawberries. It was bad but a bit of a getting-used to-experience. I think I was expecting the strawberry smoothie like I´m used to. I use a hand blender to make the shake more smoothly blended. Cocoa powder (used for baking chocolate cake) is also very good and might be good to hide the oaty taste. Some also like instant coffee, that could also cover the taste. Rice milk or ordinary milk makes it a bit more milkshake-ish.
These days my favorite Huel shake is:
1 scoop cold rice milk
3½ scoop cold water
5 grams/1 tea spoon cocoa powder
20 drops of Capella flavour (Chocolate Fudge Brownie) - leave out this and add more cocoa powder
2 gram og stevia
Everthing is added and blended with a hand blender. 