PREHEAT the oven to 400ºF. Lightly butter or spray twelve 3 x 1 ¼-inch (3 ½- to 4-ounce) muffin cups with vegetable oil spray, or line the cups with paper or foil liners.
STIR together the flour, baking soda, cinnamon, and salt, in a large bowl.
BEAT the oil and sugar with an electric mixer for 2 minutes. Add the eggs and vanilla and beat for 1 minute, in another bowl.
MAKE a well in the center of the dry ingredients and pour the liquid ingredients into it. Stir just to combine.
STIR in the apples, raisins, and walnuts, mixing only until combined. A few white streaks in the batter are fine.
SPOON the batter into the prepared muffin cups to fill them about two-thirds full. Bake for 20 to 25 minutes or until a cake tester inserted in center of a muffin comes out clean.
REMOVE the muffin tin(s) from the oven and cool on a wire rack for 5 to 10 minutes before removing muffins. Let them cool on the rack.
SERVE warm or cool completely and store in an airtight container at room temperature or in the refrigerator. (Because they contain apples, the refrigerator is a good idea, especially if the kitchen is warm.)
TIP: These muffins freeze well for up to 3 months.