RasPi Video to OLED
Without soldering, wiring or any specific hardware knowledge, you can easyly click this project together and create a viewfinder for your PIcamera.
I marked this project intermediate rather than easy, simply because installation of the libraries might cause slightly issues depending on your starting point of your Raspbian OS. From a clean installation, such as the one I described here: https://www.hackster.io/gotfredsen/raspberry-pi-weather-station-8562ad, the below should work without problems.
Check out this project on Hackster!