Peel the butternut squash and discard the seeds. Cut the flesh into 1/2-inch pieces. You should have about 2 cups of squash.

Add the olive oil to a skillet set over medium heat. Add the onion; cook 2-3 minutes, or until softened. Add the squash; cook 5 minutes, or until the edges begin to brown. Pour in the water; cook 10 minutes or until the squash is soft and the water has cooked off.

In a small dish, stir together the coconut milk, curry paste, and brown sugar. Pour over the squash, stirring so it's evenly coated. Cook 1 minute. Add the basil and cook until wilted, 1-2 minutes. Stir in the fish sauce.