This is a cheatery recipe because it is really easy. There's nothing particularly seasonal about these vegetables--it's just that they're readily available in the wintertime (thanks southern hemisphere!). They taste crunchy and fresh when prepared this way, and the bright colors are a technicolor medicine for winter doldrums, so give it a shot.
Cut one small head of cauliflower into florets of no more than 1 ½" in size and set aside. Do the same with a head of broccoli, reserving the stalks for another use (I deeply love broccoli stalks and can't imagine throwing them away, in fact I used my reserve of them last night for a delicious brown rice-tofu-broccoli stalk stirfry). Take three large carrots, peel and cut into rounds of about ¾" in width. Try to get each vegetable cut into equal sizes. Get a big pot of water up to a hard boil on the stove. While you're waiting for it to boil, fill a bowl of water with cold cold water and at least one tray of ice cubes. You are making an ice bath for your veggies! When the water is boiling merrily, put your broccoli florets in for exactly one minute. Fish them out with a wire mesh colander (or whatever, just don't drain the boiling water because you are going to keep using it) and dump the broccoli into the ice bath. This will instantly stop their cooking which will preserve the crunchy fresh flavor and the brilliant green color. Swirl them around to cool off, then fish them out and place in the fridge. Meanwhile, hopefully your water in the pot on the stove is back up to a boil again, so add in your cauliflower and let it boil for just under 2 minutes, then repeat the fish out/dump in ice bath/stick in fridge routine that you just did for the broccoli. Do the same exact thing for your carrot rounds, also letting them boil for not-quite 2 minutes. You might need to add a few more ice cubes to the ice bath to keep it chilled between vegetables. When all the vegetables are done, store them in the fridge until it's time for dinner. Serve the mixed vegetables either tossed with a delicious vinaigrette or drizzled with the Trader Joe's goddess dressing (it has tahini in it!). This also makes a great lunchbox addition or colorful finger food for little kids.