I have 2 motors attached to an h-bridge and using the serial monitor i can control which direction the motors are turning. Can i also control the speed of rotation using code or slight tweaks to the circuit?
Yes. Connect an Arduino PWM output (the ones marked with a '~') to the 'enable' pin of the L293.
You then need to analogWrite(L293_enablePin, motorSpeed); to that same pin somewhere in your code.