Try to get very small, fresh zucchini. If you grow your own, you can gently sauté the flowers first.
Zucchini is very wet, and will cook to mush if boiled. I stir fry it.
First it cut it lengthwise, then again and again so you have long skinny wedges. Then cut away all the interior, fleshy part and discard. This will eliminate most of the water and it will cook better. Then cut into inch and a half lengths.
This recipe works best if you only cook enough to serve 2 - 4 people and assumes using a 9 - 10 inch sauté pan. If you put too much in a pan, it will steam and get mushy.
Heat about a tablespoon of olive oil and a little butter to medium high heat in a skillet or sauté pan, add zucchini and stir.
After a couple of minutes I add sliced or minced fresh garlic, and salt (If you put the garlic in before the zucchini, it is likely to overcook and become bitter.) You can also add sliced sun dried tomatoes if you like.
A nice touch is to slowly fry thinly sliced Garlic in olive oil until it is light brown, remove and drain on a paper towel and add to the zucchini as you serve it.
Recently I have been cooking the zucchini, cut into disks, with wedges of fresh tomato, chopped onion and minced garlic. The tomatoes break up and as it is cooking, it seems like it has too much water, then it all seems to reduce at the time the zucchini becomes tender. Excellent. Again, don't cook too much at a time or it will simmer for too long.
Sauté in olive oil, one chopped onion until beginning to go transparent.
2-3 cups sliced zucchini
2-3 medium fresh tomatoes, cut in wedges and at least partly seeded
1 teaspoon minced garlic
Stir fry gently over high heat until moisture is mostly absorbed and zucchini is tender.