I tend to mostly cook in bulk and freeze it in portions. As long as you remember to take out what you want before you go to work, you can have a tasty, nutritious meal in minutes.
At the moment, I have chilli con carne, spag bol (tends to go a bit watery in the freezer), scouse, Thai green curry, beef stew and 3 different kinds of soup in my freezer as well as several portions of rice (I buy a bag of rice, boil the whole thing, rinse with cold water and portion up when cool).
Also, things like chops or sausages are quite quick to cook, as is fish. By the time your tatties are boiled you can have your chops/sausages/fish done and any veg you want. I also keep a selection of frozen veg in the freezer. The texture isn't as good as fresh but most veg is frozen within hours of harvesting so the goodness and flavour are still there. Frozen spinach is particularly tasty.
As mentioned above, salads are easy as well. I get the pre-packed salad bowls from Morrisons, they're only £1 a piece and you can add whatever you want to them. Things like a tin of tuna and/or a couple of boiled eggs or some sliced cooked meat or a cooked chicken breast or the like. All tasty and nutritious.
These are the sorts of things I eat most of the time but, every now and then I like to treat myself so I'll organise ingredients for something special, crack open a beer or pour a glass of wine, get my apron on and get busy in the kitchen with Absolute Radio 70s on the iPad - basically make it into an event to be enjoyed. Cooking "fancy" meals can be a bit challenging as you often need ingredients you wouldn't normally buy and supermarkets tend not to cater to singletons. As a result I have an incredibly well stocked spice cupboard and I've had to be inventive in trying to use up leftover ingredients in the days after.