Yes MOSFETS can be switched with a pulse, but they still need current to drive them. A MOSFET like the one we are talking about will have a relatively large parasitic capacitance, when you switch the MOSFET this needs to be charged up that takes current. The faster the switching the more current you need. The maximum output current from your opto-coupler will probably be quite small, depends on what you use have you decided yet?? So the current from the opto-coupler device wont be large enough to properly drive the MOSFET.
A driver circuit for a MOSFET just consistos of two or three smaller transistors used to amplify the current from the opto-coupler. I haven't got a schematic editor available at the moment so I can't give you a circuit. They are very simple maybe someone else can suggest one.
I looked at some opto-isolators some of them are designed specifically to drive MOSFETs directly, two of these are TLP250 and TLP251. They have sufficient output current to drive the MOSFET directly (you will need a resistor between the output of the opto-isolator and the gate of your MOSFET).
Does this clear it up a bit?