1Bring a large pot of water to a boil. Thaw the green beans (or warm in the microwave). Cut the potatoes into 1/2 inch cubes.
2Determine how long the potatoes and pasta will need to boil before adding the beans.
1/2" cubed potatoes will need 15 minutes.
The pasta will need somewhere between 8 and 12 minutes -- exact time needed can usually be found on the package.
Subtract the minutes needed for the pasta from 15 and this is how long you will wait between starting the potatoes and adding the pasta.
Subtract 5 minutes from the time needed for the pasta and this is how long you will wait between adding the pasta and adding the green beans.
For example, if the recommended cooking time for the pasta is 10 minutes, start the potatoes - boil 5 minutes - add the pasta - boil 5 minutes - add the beans - boil 5 minutes, for a total of 15 minutes boiling.
3Drain the potatoes, pasta and beans. Optionally, toss them in a bit of olive oil to add flavor and prevent clumping.
4Stir together the yogurt and pesto and fold into the drained mixture. Fold in the parmesan a little at a time to prevent clumping. Add salt & pepper to taste.
5Serve hot or chill and serve as a potato-pasta salad.