USB power is really quite limited. As well as motors made for your particular application, if you can go to 12 volts you could look at the motors used for rotating reflectors on automobile warning beacons or disco lights.
However, USB powered turntables for light loads are available quite cheaply. (Example Amazon link)
A microwave motor would probably require more tinkering than at first appears, if it could be made to work at all.
If you do a google search for "DC gearmotor 5v" you'll find hundreds of much more suitable options, perhaps such as this one.
Microwave motors that I have seen are AC motors. There are very small motors with attached gears that might be suitable. They are sold for hobby and educational use.
Most of the power is lost in the motor and gear. The electrical input power will probably be more that twice the mechanical output power. A 5 volt USB supply may or may not be able to supply ...