A circuit that will produce one pulse over a given time period, independent of the number of input triggers received by the circuit. The rest is open game, just specify the limitations or requirements of the circuit.
There's usually more than one way to skin a cat, I'm wondering what other ways there are that I don't know about.
There are lots of options, but an integrated timer chip, whether it be the ubiqutous 555 or one of the other integrated solutions, will be the simpliest to implement.