When zucchini's in season -- right about now -- it's everywhere. Every summer, vegetable gardeners (and CSA shareholders) face a few weeks when it comes so quickly that keeping up with the supply seems to require eating it at almost every meal, or at least daily.
I can see eating it at breakfast, sometimes at least, but three times a day still seems a bit much. Nevertheless, zucchini is an incredibly congenial vegetable, mild in flavor, pleasantly firm, and juicy. It takes well to almost every cooking method you can think of: steaming, sautéing, roasting, grilling, frying, even braising. You can even eat it raw in salad, or as a cucumber substitute; you can shred it and bake it in bread; you can simmer it in soups. It also plays wells with others, which is why it's a mainstay in mixed-vegetable dishes like minestrone, ratatouille, and vegetable curry. It's forgiving, too; even if you overcook it, it never turns objectionably mushy or bitter, but just becomes more and more tender. (All of this, and the below, goes for yellow squash as well, which can always be substituted for zucchini, and vice versa.)
More benefits: Zucchini requires no special preparation before cooking; all you have to do is cut off its ends. No peeling (ever, and the skin is ever-so-slightly different from the meat), and no seeding (if there are loads of seeds, which means you have a huge one on hand, it isn't going to be terrific -- but there's nothing you can do about that). You can salt it if it's especially limp, but this shouldn't be a problem in summer, when your zucchini should be fresh and local. And slicing, dicing, or chopping zucchini is a pleasure, because it yields easily and satisfyingly to pressure from a chef's knife. (For uniform, thin slices, nothing is better for zucchini than a mandoline.)
Even though there are a million things you can do with zucchini, some are better than others, at least in my world: I find myself turning to a couple of fast, easy, and delicious treatments over and over again. The first turns zucchini into a pasta sauce. I've probably converted just about every vegetable into a pasta sauce at least once, but zucchini is especially good; sautéed in olive oil until just tender, its texture becomes similar to that of properly cooked--that is, al dente-pasta.
You can spruce up pasta with zucchini by adding other vegetables (tomatoes are an obvious choice, though green beans, bell peppers, and/or mushrooms are all good) or cheese (ricotta is traditional and wonderful), but I happen to love pairing sautéed zucchini with a carbonara-like sauce made with bacon, eggs, grated Parmesan, and mint or basil. Zucchini and the herbs counterbalance the classic animal ingredients, turning pasta carbonara into a dish light enough to serve on a warm summer evening.
My other favorite thing to do with zucchini is to grate it, then combine it with just enough flour and egg to make a batter that holds together. Pan-fried in olive oil, this makes pancakes that are wonderful, seasoned just with Parmesan, salt, and pepper, but with the addition of shallot, garlic, and thyme, they become more fragrant and elegant than your average vegetable fritter. Serve these as hors d'oeuvres (just make them bite size instead of burger size), as a main-course with a simple green salad, even as a sandwich filling. In other words, you could actually serve these at every meal -- and you might actually want to.