As long as piggies are fed plenty of hay, some fresh grass and a variety of fresh and dried forages and a variety of veg so they get a balance of nutrition, then it is actually acceptable to not feed pellets at all. However, they are given as a way to ensure all nutrition is met in case the diet is lacking in variety etc.
I only give pellets three times a week in summer (I give them five times a week in winter when they aren’t on grass daily) and instead give fresh and dried leaf forages in the place of pellets
You wouldn’t want to make fruit a major part of the diet in any event