Heat oven to 350 degrees F and coat a 12-count non-stick muffin tin with cooking spray.
In a large bowl, combine the oats, milk and pumpkin puree. Stir until there are no lumps of pumpkin. Let soak about 5 to 10 minutes, or until most of the liquid is absorbed.
To the oat mixture, add the maple syrup, egg, canola oil, baking powder, cinnamon, ginger, nutmeg, cloves and salt. Stir until thoroughly combined. Stir in the chocolate or chocolate chips.
Fill each muffin cup with approximately 1/3 cup of the batter. Bake for 30 to 35 minutes or until lightly browned and tops spring back when lightly touched in the middle on top. Cool in pan for 10 minutes, then remove to cooling rack.
Refrigerate leftover muffins for up to 2 days or freeze for up to 3 months in an air-tight, resealable bag.