Preheat your oven to 350°F. Line a baking sheet with parchment paper.
Slice each croissant in half lengthwise. Place the bottom halves on the prepared baking sheet.
In a mixing bowl, combine the chocolate chips, chopped nuts, granulated sugar, and ground cinnamon. Mix well.
Drizzle the melted butter and vanilla extract over the chocolate mixture and stir until combined.
Spoon the chocolate mixture evenly over the bottom halves of the croissants. Place the top halves back on the croissants.
Bake in the preheated oven for 10-12 minutes, or until the croissants are golden brown and the chocolate is melted.
Remove from the oven and let cool for a few minutes. Dust with powdered sugar before serving, if desired.