Place a 7x11” glass baking dish in the oven and preheat to 400°F.
Measure the vinegar into a glass measuring cup and add enough milk to measure 1 cup liquid. Stir and let stand a few minutes to thicken (you are making instant buttermilk, which gives the bread a tender crumb). In a medium bowl, combine the pumpkin, eggs, ¼ cup olive oil, and molasses and whisk to blend. Whisk in the milk mixture.
Combine the cornmeal, flour mix, brown sugar, baking powder, salt, baking soda, xanthan gum (¼ teaspoon if using Cup4Cup, ½ teaspoon if using other flour mixes), ginger, allspice, and a generous amount of pepper in a small bowl and whisk to blend. Add the dry ingredients to the pumpkin mixture and mix until evenly combined. Stir in the dried cranberries.
Remove the baking dish from the oven and brush with oil to coat. Add the batter and spread evenly. Using a hot pad, return the pan to the oven. Bake the bread until brown, springy to the touch, and a toothpick inserted in the center comes out clean, 25-30 minutes. Cool in the pan on a rack at least 30 minutes. Serve warm or at room temperature.