Pour cake mix into a large bowl. Make a well in the center and pour in milk, eggs, and vegetable oil; stir until well combined. Pour boiling water into the batter and stir to mix.
Pour batter into a slow cooker.
Combine avocados, almond milk, honey, cocoa powder, and vanilla extract in a food processor; blend until the consistency of pudding. Pour over the batter in the slow cooker. Sprinkle chocolate chips on top.
Cook on High until edges have pulled away from the sides of the cooker, about 2 1/2 hours.