Hey man,
I mentioned this in a seperate thread on here but here is the simplified facts of any weight gain or weight loss:
Your body has a fixed amount of calories it requires to sustain itself. If you are neither gaining weight nor losing weight, this amount is likely to be what your daily intake is now.
If you eat more calories than your body requires, you'll gain weight as stored fat, if you eat less, you'll lose weight as fat and muscle is burnt for energy.
For now, track what your daily intake is in calories without changing anything to find out the base amount of calories you body requires. Do this for a week, 2 weeks to be accurate. Generally the amount your eating each day should all be within 100 kcals of each other, you may have a sparse spike on odd days. This is your standard set calorie amount. To gain weight, aim to chuck about 500kcals on top of this per day.
So without even going to the gym, you'll steadily gain weight by this theory.
If you do go to the gym, things get a little more complicated. When your lifting weights, you'll be burning calories. So your standard set amount of calories per day should go up to account for burnt calories. Your body will also have different requirements, such as requiring more protein to help repair your muscles after a weights session.
So you can adjust your diet accordingly, from the sounds of it, your diet is nigh spot on, you just need to eat more. Keep with the Chicken (breast), beef and fish for protein sources, I'd reccomend a form of protein powder for after the gym as this will be greatly beneficial for the anabolic hour after weight training when your muscles will want protein (personally my preference is the Phd Pharma Gain blend or Optimum Nutrition Gold standard whey, but it depend on your preferences, everyone works a little differently).
Stick with the rice and pasta, sweet potato is anothrr good carb. Baked potatoes have their benefits too.
Most importantly, Vegtables. Broccoli, asparagus, peppers, onions, tomatoes, spinach, carrots etc.. get a good mix in daily. Aim for a good mix of fruit, banana smoothies are the way forward in my oppinion.
From there, you should gain some good, healthy weight. Obviously do some more of your own research into the area, but that's a simplified version of weight gaining.
There's some more information and motivation on my blog:
beremarkableorbeforgotten.blogspot.com
Or feel free to pm me for any other info.