One of the many, many, many frustrating things about Windows 10 is its forced automatic updates that it pushes to its users. Recent patches have given you "options" in choosing what time of day you would prefer to have these updates shoveled, but no actual control over install or restarts.
There is, however, a neat trick to take back control of your system: Metered Connections
Having your connection pegged as Windows decides to feast on your bandwidth is bad. Having it download gigabytes of data over your limited data cell network is worse. This is why Windows 10 has the option to set every Wi-Fi network as a "Metered Connection". Connections marked as Metered will not download updates automatically, allowing you to choose when and where your computer should be updated. Anarchy!
Note: Be certain to mark all of your current and any new hotspots as Metered. If you forget one, your system will latch on and auto-update as soon as you connect to it.
To add change a connection to metered, start by launching the Windows 10 Settings panel.
Click "Network & Internet"
Click "Wi-Fi" on the left-hand list
Click "Manage known networks"
Click "Properties"
Finally, click the toggle to "Set as metered connection"
And that's it! Repeat the process to disabled Metered when you want your system to update.