In a nutshell: Greece would put state assets into a fund, sell that fund to the EU for 125 BN EUR and the EU would commit to spend 20 BN EUR to bring those assets into good shape. Then these assets would be privatized (time frame about 10 years) and privatization gains of 40-60 BN EUR would be expected. These gains would go back to Greece.
Greece would use the 125 BN EUR to buy back her own debt. Such debt currently trades around 30% of nominal. If Greece could buy back her debt at that discount, the 125 BN EUR would be enough to make Greece debt-free (this is a bit of an exaggeration; in practice Greece will have to pay far more than 30% of nominal but, at the same time, far less than 100%).
The 20 BN EUR upgrading investment by the EU would in and by itself already be an enormous stimulus for the economy. Add to that the new momentum which the economy would experience by being able to focus on future potential instead of worrying about past debt all the time and you can expect a steep recovery.
Is there a catch to this? Not really. Well, there is one minor catch.
That minor catch is that the government will no longer have control over a rather large sector of the Greek economy. It will no longer be able to use the resources of those companies for political purposes. That is, of course, very sad for the government. On the other hand, the government will no longer have to pay for the deficits of those companies and that, in turn, is very happy news for Greek tax payers.