Bring a large pot of water to boil and add green beans. Allow to cook 3-4 minutes.
Remove from heat, drain beans, and immediately rinse with cold water. Pat dry.
In a large skillet, heat 1 tsp. olive oil over medium high heat. Add the green beans and toss to coat a minute or so, until heated through.
Remove from heat and toss with as little or as much pesto as you like. Sprinkle with Parmesan and serve warm.
Or refrigerate and serve cold. It's good either way.