Preheat oven to 350 degrees. Line a baking sheet with parchment paper. Set aside.
In a food processor, process the ripe plantain until smooth. Scoop out the plantain into a medium mixing bowl. Add the arrowroot powder, cassava flour, avocado oil, canned coconut milk, baking soda, baking powder, and sea salt. Stir slowly using a large mixing spoon until mixture forms a dough ball. (Will appear sticky, but will easily roll in hands.)
Scoop dough out using a spoon and place into 8 equal-sized dough balls. Shape into round plump buns. Bake for 20-25 minutes or until light golden brown on the bottoms.
Remove from oven. Let cool for 5-7 minutes. Cut lengthwise making a sandwich bun.
Store leftovers in an airtight container for up to 3 days.
For freezing: Make dough and roll out into buns. Place each uncooked bun onto a piece of parchment paper. Place into a freezer container or baggie. When ready to bake, remove from freezer, thaw, bake according to instructions above.