Magic Fruit-and-Veggie Cupcakes

Cooking spray (optional)
1/2 cup all-purpose flour
1/2 cup whole-wheat flour
1 tablespoon soy flour
2 tablespoons wheat germ
1/2 cup bran flakes cereal or old-fashioned oats (or a combination)
1/4 cup ground flax seeds
1 teaspoon baking soda
1 teaspoon baking powder
1 teaspoon ground cinnamon
Pinch of salt
1 large egg
1/4 cup packed light brown sugar, plus more for topping (optional)
2 tablespoons extra-virgin olive oil
1 teaspoon vanilla extract
2/3 cup plus 1 tablespoon whole milk
3/4 cup grated or finely chopped vegetables (carrots, zucchini and/or spinach)
3/4 cup grated or finely chopped fresh or dried fruit (apples, pears, pineapple and/or raisins)