Because grains such as white rice, pasta, and sandwiches are easily digested, you will be hungry afterwards, and you will tend to overeat them. So within this week, just replace the chicken sandwiches with chicken (peeled) and fruits, and challenge to replace cereals with vegetables. Vegetables are slower to digest than cereals, and they can also drain excess water to achieve a slimming effect.

In my opinion, although replacing food with vegetables is very necessary, you should not cut it out completely, but should maintain good carbohydrates to ensure enough nutrients needed for the body.

Yes, you should not replace food groups entirely. Weight loss can be easily achieved with a calorie deficit (caloric input < caloric output), but maintaining results is the hard part. Ensure that the changes you make to your lifestyle are not too drastic and practising good habits is key to sustainable fitness. I came across this article and thought you may be interested to give it a read: What Type of Diet Works For You?

I love vegetables.