These tasste great, not too sweet, packed with healthy, nutritious ingredients.
Preheat oven to 400 degrees. Spread walnuts on a baking sheet and put them in the oven when you turn on the oven and turn on the timer for 10 minutes. Take pan out of the oven and allow nuts to cool while you finish assembling the rest of the batter, then chop.
Spray a 12-cup muffin tin with cooking spray.
Meanwhile, whisk together the dry ingredients, flour through salt and also walnuts,* in one bowl, In another bowl large enough to mix the whole batch of batter whisk together the wet ingredients including the apples.
Quickly fold the flour mixture into the wet ingredients,** then add the chopped walnuts. Divide batter between muffin cups and bake for 15 minutes, then test. They may need a few more minutes. Eat while warm if possible, but leftovers freeze well and can be reheated in the microwave.
*I have you mix in the nuts with the dry ingredients before adding that mixture to the wet ones because you want to get the muffins into the oven as soon as possible after the liquid comes into contact with the leaveners with as little mixing as possible. Putting the nuts into the batter separately means that you have a separate step, and you can cause your batter to deflate. I notice a real difference in how well my muffins rise if I mix as little as possible. I think, by the way, that this deflation problem is the real reason why you shouldn't overmix your batter; you'll often see that gluten development is the issue, but as far as I'm concerned it's the loss of leavening.
**I disagree with another common notion: that you should do the mixing the other way around, adding the wet ingredients to the dry. It's very hard to get all of the flour incorporated when you do it this way. Do be sure to scoop from the very bottom either way you do it, though. And don't use a mixer! Use a flexible spatula and mix as gently as you can while getting everything incorporated.