Preheat the oven to 375 degrees F and coat a 24-cup mini muffin pan with cooking spray. Slice the chorizo into 24 rounds, about 1/2 inch thick.
Heat the vegetable oil in a large nonstick skillet over medium-high heat. Add the chorizo and cook, stirring occasionally, until lightly browned, about 3 minutes. Transfer to a paper towel-lined plate to cool.
Meanwhile, combine the cornmeal, flour, sugar, 1/2 teaspoon salt, the baking powder, baking soda and cayenne in a large bowl. In another bowl, whisk the egg and buttermilk, then whisk into the cornmeal mixture along with the scallions until smooth. (It should be the consistency of pancake batter.)
Pour the batter into the prepared muffin pan, filling each cup about halfway. Place a piece of chorizo in the center of each cup. Bake until golden and cooked through, about 12 minutes. Let cool 5 minutes, then remove from the pan.