Need ideas for UI to cast spells

Hi all!
I work on Yeti Home Defence game - details here -
https://forum.unity.com/threads/yeti-home-defence-not-usual-tower-defence-game.686725
And need your ideas about ui to select in-combat cannon and magic spell from not short list.

For spells:
Initially my intention was to create magic book--like ui, but it would put hot combat on pause every time you want to cast spells

Next idea is to use gestures like in Eternium game , eg Z for first attack, O fir second etc
It is possible because all magic would be area size, no target need

For cannon, gamer should touch one point to fire, so gestures are not suitable, so I need somehow let him select bullet type from 3-4 options quickly
Radio group-like ui?

What do you think?

 

2nd question: is there ready unity code for gestures recognition?