The key word here is versatility.
Like the Flashes, there are, of course, a number of Green Lanterns – all of which should easily defeat the Hulk – but we’ll be focusing on classic Hal Jordan here.
Hal has a list of feats as long as Plastic Man’s fully-stretched arm and the range of what he has done with his Power Ring is absolutely insane. He has so much in his arsenal to defeat Hulk that it’s basically ridiculous.
First of all, he has the power to easily contain the Hulk. His constructs have contained the power of exploding stars (see below and click the image to make it bigger), so the strength of the Hulk should not enable him to escape one of them (his constructs have been large enough and strong enough to both hold and move entire planets).
But in terms of his versatility, we could go on all day. Hal can turn himself invisible, his constructs can slice through characters as durable as Amazo and Mongul II like a hot knife through butter, he has reignited dying stars with his ring’s energy, he has destroyed planets with energy blasts, he has transmuted matter with his ring (he could turn Hulk into a teapot!) and he has both augmented his own strength and speed (enough to keep up with Flash).
In a nutshell, he has so many options to choose in order to defeat Hulk that it would be a cakewalk (we’ve barely touched the sides of what his ring is actually capable of). His only problem might be choosing which option he’s going to use!