My daughter will only eat one or two slices of a raw apple but will eagerly scarf down an entire apple when it's steamed. Steaming the apple requires minimal effort and makes it soft and a little more sweet. These are the simple steps I take:
1. Core and slice - don't worry about he peels, they come off easily once it's steamed.
2. Place the slices in a steamer basket and put the basket in a saucepan with a few inches of water (don't let the water touch the apples).
3. Cover and bring to a boil over high heat. Let it boil until the apples are tender and can be pierced easily with a fork (about 5 minutes). You can very gradually keep them in for less time to get your child used to a harder texture and work up to raw apples.
4. Let it cool and peel the skin if desired. I encouraged my daughter to peel the skin herself to give her some extra exposure with it and because it's an awesome fine motor task! Eventually I will encourage her to try some bites with the skin on.
With the exception of the one slice she reluctantly gave up to her baby brother (another bonus - good for babies!) she devoured an entire apple in a couple minutes and asked for more!