You will need to build up your base mileage to allow you to reach your goal. At the same time as including long runs in your training you will need to include some speedwork and tempo runs.
I wouldnt worry too much about your times at the moment, or including speedwork - you should really focus on increasing your stamina and distance you can run. Once you have a good base then focus on some speedwork. There are some great beginner training plans on this website,and you could also have a look at RW smartcoach.
I would try to incorporate more protein in your diet, it will help you satiate your hunger. A good example would be to have eggs for breakfast (poached or scrambled with toast) at lunch a great option would be a salad with lean protein plus a small amount of carbs. Studies have shown that eating this meal at lunch will prevent your afternoon energy dip! The hard thing is to plan in advance - as it seems you are time deprived whilst at work!