In a large stock pot, heat oil. Add onion, thyme and pepper and saute for 2-3 minutes, Add coconut milk, water, salt fish, green seasoning and bring to a boil. Break salt fish into chunks and add to pot. Add cassava, sweet potato, eddoe to the pot then add plantains on top and cook for 20 minutes.
When plantains are tender, remove and continue to cook until the other vegetables are tender.
While the vegetables cook, make the duff.
Place all purpose flour, sugar, salt and baking powder in a bowl and mix to combine. Add room temperature butter to the flour mixture and rub in the butter.
Add water and mix to form dough; let dough sit for about 10 minutes.
Roll dough into logs about the size of a finger then press gently in the middle. Place duff into pot.
Cover the pot and cook for at least 5 minutes. Do not open the pot or the dumplings will fall and become dense.
Turn heat off, Remove duff from metemgee. Serve metemgee with duff.