In a small pot, bring ⅓ cup non-dairy milk and ½ cup chocolate chips to a low or low-medium heat. Stir almost constantly with a fork or whisk until the chocolate chips are fully melted and smooth. (It should take just a few minutes.)
Stir in the peanut butter and maple syrup. Once it has all completely combined, continue cooking and stirring while the sauce reduces and becomes the consistency of gravy. You want the sauce to be creamy but still pourable. If it gets too thick or seizes up, stir in another splash of non-dairy milk. Remove from heat and set aside.
Heat the outdoor or indoor grill to 500 degrees. Lightly brush the grill grate or the cut side of the bananas with oil.
Place the bananas cut side down on the heated grill. Don't move them for about three minutes, until they get good, dark grill marks.
Use tongs to flip the bananas onto the back where the peel is still attached. Continue cooking them for another two or three minutes until the peel has darkened and the banana has softened. Move them to a plate to cool slightly.
Put out 4 bowls or banana boats. Into each bowl, put 2 or 3 scoops of vegan ice cream. Remove the peels from the bananas. Put two banana halves into each bowl. Top with warm chocolate peanut butter sauce. Garnish with chopped peanut butter cups. Serve immediately.
Video
Notes
Make ahead instructions: If you're not using the chocolate peanut butter sauce right away, store it in the refrigerator in a covered glass container. It reheats well in the microwave before serving. Just add a splash of non-dairy milk, heat in the microwave for about 30 seconds, and stir until smooth again.