1. Lightly coat a 9-by-13-inch rimmed baking sheet with nonstick pan spray. Line the baking sheet with parchment paper, allowing the ends of the paper to hang loosely over the short edges of the baking sheet.
2. In a large bowl, add the semisweet and bittersweet chocolates and the salt. Fill a medium saucepan with 1 inch of water and bring to a boil over high heat. Reduce the heat to low and place the bowl on top of the saucepan (make sure the bottom of the bowl doesn’t touch the water). Stir the chocolate often until it is completely melted and smooth, 3 to 5 minutes. Remove the bowl with the chocolate from the saucepan.
3. To the melted chocolate, add ½ cup of the granola and stir to combine. Pour the chocolate-granola mixture onto the prepared baking sheet and use a spatula to spread the mixture in an even, ¼-inch-thick layer. Immediately sprinkle the chocolate with the remaining ¼ cup of the granola, the cacao nibs and the crystallized ginger and refrigerate until hard, about 1 hour.
4. Remove the bark from the refrigerator and use the parchment overhang to lift it out of the baking sheet and set it on a cutting board. Use a sharp knife to break the chocolate into pieces, then serve immediately or store in the refrigerator for up to 2 days.