To answer OP’s question, I use Cyclemeter on iOS. It is also available for Android. You can make custom screens as simple or complicated as your heart desires.

First shot is what I see when riding. I can swipe over to the next screen for more detail.

You can also easily set up a heart rate specific display. I usually know where I’d like to be for my own zones when training. But, I do like the nice summary at the end of the ride showing the duration and percentage of the ride spent in each zone.