If ZAP is displayed in a really tiny window then its probably because you have a high DPI display.
The solution is easy - use Java 9+
If you need to have multiple versions of Java on Windows then you may find it difficult to specify which one should be used. However changing the last line of the existing zap.bat batch file to specify the path to the right version of Java should solve this problem, e.g.:
"C:\Program Files\Java\jdk-11.0.1\bin\java" %jvmopts% -jar zap-2.7.0.jar %*
If you can only use Java 8 on Windows 10 then you can set the compatibility settings:
Finally, if all else fails, you can increase the Font Size via the ZAP Options / Display - this will also scale all of the images as well, although some graphical elements such as checkboxes and tree expand/collapse controls may not scale.
If none of these solutions work for you then raise an issue stating exactly which system and versions of Java you are using.