I am working on an electric bike project and have quite a big TFT / LCD screen.
Previously I used simple methods to build my UI (drawline() etc.).
This does work fine but obviously isn't very pretty 
This very crudely captured image shows a portion of the "background" elements of my current UI:
As you can see, I have upgraded to a new display, therefore the UI isn't scaled properly. I don't necessarily want / require scaling. No touch-screen is used.
I would like to draw such a "frame" (or multiple smaller ones) which is / are later filled with data.
I have looked into ways of displaying pre-made images on the screen. One way to do it, which is very common, would be to create an image file on the PC and then convert it to an array of bytes.
Which software is best to design such an UI?
There are some options available online but all seem to be oriented towards another audience (mostly App and Web development.