Line a baking sheet with parchment paper and set aside.
Place white chocolate in a heat-proof bowl and place over a pot of boiling water.
Whisk the chocolate until melted, about 2 minutes.
Once chocolate is melted, scoop into the center of the lined baking sheet.
Use an offset spatula to spread the chocolate into a 1/4" thick rectangle.
Place the green candy melts in a microwave-safe bowl and heat for 25 seconds. Stir and reheat as needed.
Place the green candy melts in dollops over the white chocolate and use the offset spatula to marble the chocolate and candy melts together.
Immediately distribute all of the marshmallows evenly over the bark and then garnish with sprinkles.
Allow chocolate to set for 1 hour before cutting into pieces and serving.