Pre-heat oven to 400 and use a standing mixer on medium low speed.
Mix oil and sugar until combined.
Add eggs and vanilla and beat until just mixed.
Add flour, baking powder, baking soda, cinnamon, and salt, a little at a time and mix until evenly moistened.
Add pumpkin puree and mix until just blended.
Set aside 1 cup of the pumpkin batter in a medium bowl.
Melt chocolate chips in microwave, stirring about every 25 seconds until chips become thick and creamy, 70-75 seconds in all.
Add the melted chocolate only to the 1 cup of pumpkin batter, mixing completely.
Pour that chocolate/pumpkin mix onto the center of the plain pumpkin batter.
Use a large spoon to fold the chocolate mixture into the plain pumpkin batter by pulling the spoon down through the chocolate into the pumpkin. Scoop the spoon from top to bottom and bring the pumpkin to the top. Turn the bowl a quarter turn after each scooping motion. Do this only 3-4 times, just until a swirl effect has been created. (More than that will create a solid chocolate look, rather than a marbled effect.)
Divide mix evenly among 6 jumbo greased, floured muffin tins (or use jumbo baking cup papers)
Divide topping equally and sprinkle on top of the muffins,about 2 teaspoons each.
Bake 20-25 minutes in center of oven - until toothpick inserted into center comes out clean, muffins are springy to the touch, and lightly golden brown. Remove muffin tin from oven and let cool on cooling rack for 5 minutes. Use two forks to gently remove muffins from tin to finish cooling on the cooling rack.