@Soecara brings up some very good points.......as usual. And, there are many other veggies that you can feel daily if you are looking for variety.
I will tell you that I feed essentially the same "salad" every day and my cavies are just as excited each time their dinner arrives. I feed spring mix, bell peppers, green beans, and either red cabbage or radicchio. When other vegetables are in season, I may add or substitute other items for variety. I also feed cucumber, celery leaves, dandelion greens, corn husks, or other suitable items. My cavies don't like many of the things that others feed such as tomatoes, zucchini, cilantro, most fruits with the exception of canteloupe or watermelon rind with a little of the flesh attached. And, I rarely give them carrots simply because of the sugar content.
If you feed too many vegetables and too often, your cavies simply won't eat enough hay to keep their teeth ground down and once they develop malocclusion, you have repeat dental bills usually for the rest of their lives. I had a painful experience with this.
Again, I echo the idea of feeding once a day.....I feed my boys about 6pm in the evening. I should mention that they have pellets available 24/7 and I have never had a problem with their weight. Oh, yes, if you ever need to go away, you are unlikely to find anyone to come over and feed your piggies more often than once per day. One becomes a virtual cavy slave in that you have to be there morning and evening to feed them.
If my boys get hungry and whine for a snack, I usually give them corn husks, radicchio or dandelion greens......anything that won't put weight on them. It seems that there is almost a predetermined time that they get hungry and it is around 2-3pm. At that point it has been a long time since their dinner, and they are satisfied with just enough food for a snack.
Don't drive yourself crazy with creating the perfect menu for them....they won't know the difference. Make it as simple as possible.