In a large mixing bowl, whisk together the soy milk and apple cider vinegar. Let sit for about 1 minute until the milk begins to curdle and separate to create the vegan buttermilk.
Next, add in the pumpkin puree, olive oil, cane sugar, brown sugar, and vanilla. Whisk with the vegan buttermilk until smooth.
Once the wet ingredients are mixed, add the dry ingredients to the mixing bowl starting with the flour and adding the pumpkin pie spice, baking powder, baking soda, and salt on top. Then, use a whisk or spatula to GENTLY mix the batter just until all streaks of flour are gone. A lumpy batter is okay at this point!
Finally, add ¼ cup of the chocolate chips to the bowl and use a spatula to gently fold them into the pumpkin spice batter.
Fill a muffin tin with 6 cupcake liners. Use a cookie scoop to add the batter to the 6 muffin liners until each is almost completely full with batter, but not overflowing.
Next, sprinkle the remaining ¼ cup of chocolate chips, pepitas, and optional turbinado sugar on top of the muffins. Then, preheat the oven to 350F and let the batter rest in the muffin tins for at least 5-10 minutes (this resting time helps form higher muffin tops!).
Once the oven has preheated, add the tray of muffins to the oven and bake for 20-22 minutes until fluffy and cooked through.
Remove the tray from the oven and immediately remove the muffins from the muffin tin. Then, place them onto a wire cooling rack. Do not let the muffins cool in the tin or they risk getting soggy on the bottom.
Once the muffins have slightly cooled, serve warm and enjoy!