My diet plan right now is oatmeal w/ lowfat milk for breakfast, snack on yogurt, some meals I have creamed spinach on a slice or two or bread, tuna, and when I feel lazy or wanna cook lunch at work I have a lean cuisine. For dinner it just depends but none of my meals are over 350 calories max unless I eat out, one or two times a month, it might be around 500. I average 1100 calories a day & workout 4-5 days a week. Is this a good plan? I also drink tons of water. Ive lost5 lbs in the first week

Hey ladybug,
It may be a good place to start, depending on where you are coming from. However, keep in mind that calorie intake is NOT all that is important in weight loss. For instance, check out the bodybuilding/fitness community. The standard diets used by female fitness competitors to get VERY lean includes 3-5 small meals per day, emphasizing lean proteins such as chicken, fish, eggs, and beef, along with a serving of veggies at EACH meal. This is time tested and works. I guarantee you will not find very lean fitness women eating lean cuisines and other processed foods to look that way. I highly suggest checking out some of their eating approaches to get the "skinny" so to speak on what works.

Really you should stray away from those types of pre-packaged and processed foods because they're ultimately filled with preservatives that elongate shelf life in the store, but shorten human life. However, it's not going to throw off your entire diet plan if you don't have time to get anything else at work, forgot your lunch at home, didn't have any food at home to bring, etc.
With food in regards to weight loss, you should eat 5-6 smaller, healthy meals per day rather than 3 bulkier meals that allow for snacking and cravings of food you're essentially trying to avoid. However, I'm not saying you can't snack on yogurt, that's great for you, I mean it in a way that a lot of people who abide by the "don't eat after six" rule who eat a dinner at 5:00 are more likely to have a craving of ice cream by the time 9PM rolls around. Instead, you could have dinner at 6:00, have a snack such as yogurt like you mentioned, an apple, fruit salad, etc. later in the evening.
Also, try to incorporate more fresh fruits and vegetables, preferably more vegetables seeing as fruits have quite a bit of sugar. However, it's not a reason to avoid fruits ultimately because fruits like apples are high in fiber which is excellent for digestive health while additionally it's very good in reducing cholesterol and prevention of having elevated cholesterol levels in general. Spinach has the same benefit, with its fiber it actively fights cholesterol because physiologically fiber attaches to it and essentially destroys it.
Drinking plenty of water is always a good thing, but you don't have to be a plant. Teas (iced, green, etc.), chocolate milk (is great after a workout, it's interesting if you'd like to Google it), and 100% juices not from concentrate are also other healthy options to intake as many nutrients and antioxidants as possible.
And just in general, weight loss is 80% diet and 20% exercise and I'd recommend trying to jog three times a week in addition to your diet and you'll find the weight to just burn off. However, getting accustomed to jogging is fairly difficult and isn't the simplest thing to ease into, however, even by using a simple interval training plan it can help you strengthen your muscles (burns fat quicker) and keep your body toned and healthy. If you're a beginner runner or have no experience, try a plan as simple as this:
(1) Walk briskly for 10 minutes/Warm up
(2) Jog 1 minute (3) Walk 2 minutes
(4) Jog 2 minutes (4) Walk 1 minute
(5) Jog 1 minute (6) Jog 3 minutes
(7) Walk briskly for 10 minutes/Cool down
Even by doing that three time a week, you can see significant changes while additionally losing weight from your dietary ramifications. Really, it's all just a learning process that's gradual and you must allow your patience to recognize the time it takes to healthily and effectively lose weight, get into shape, and reach optimal success through exercise and diet combined.
Just remember there's not a single thing worthy in life of possessing without a genuine struggle and I'm absolutely confident that you can reach your goal, just as long as you are.
Best of luck to you.