Preheat the oven to 350°F. Line an 8½-by-5-inch bread pan with parchment paper.
To make the brownies, place the roasted hazelnuts, walnuts, macadamia nuts, vanilla, honey, powdered sugar, cocoa powder, and salt in a food processor.Process for about 15 seconds, stop and wipe the sides down, then process again just until the mixture is smooth and shiny.
Pour the mixture in the prepared pan and press it down to create an even surface. Cover the pan and place the mixture in the refrigerator for several hours, or overnight.
To make the chocolate ganache, whisk the coconut oil, cocoa powder, vanilla, honey, and salt together until it is smooth and fluffy. The ganache can be spread on the brownies right after they are made or after they have chilled.