Oh goodie you have a microwave and a fridge to work with!
I love making vegetable soup and taking the leftovers to work. You can spoon it over rice or pasta in a thermos, put it in the fridge when you get to work, and zap it for two minutes at lunchtime. You can do the same thing with bean chili, or any kind of pasta dish. Leftovers are key - cook a lot for dinner, and take half the next day for lunch.
How about a veggie wrap? Don't assemble it the night before because it will get soggy. Pack a big tortilla, a little tupperware container of hummus, some slices cukes and tomatoes and lettuce leaves, whatever veggies you like. Chill it in the fridge. It will take two minutes of your lunch hour to assemble it into a big, yummy wrap.
Do you have a freezer at work? Sometimes I get frozen vegetarian burritos and take one to work for a quick snack or meal.
I also like to bring a tupperware bowl of cereal or granola and a small single-serving size or rice or almond milk.
For snacks, I like to bring cut-up veggies and pretzels or pita chips with hummus or any kind of bean dip. I also keep a box of granola bars, a jar of peanut butter and some crackers in my desk, just in case. Peanut butter is GREAT if you're trying to go high-calorie and gain some weight. So is olive oil, so drizzle it over pasta and salad and cook with it often.
Now I'm all hungry