Wash the borage and chard. Blanch them in the boiling water for 2 minutes. Strain and set aside to cool for a few minutes, then vigorously squeeze the greens of all their liquid (I find it easiest to do this by using a fine-mesh strainer). Roughly chop the squeezed greens. Keep the pot of water boiling. Whisk the eggs together in a large mixing bowl. Stir in the Parmesan, bread crumbs, diced onion, garlic, nutmeg, herbs, and salt. Mix well to combine. Stuff the cavity of the chicken with this filling. If you have any filling left over, you can form it into little balls, sprinkle them with some additional Parmesan, bread crumbs, and a generous amount of olive oil, and bake them in the oven at 425 degrees F until crispy and browned, about 30 minutes.