In a large saucepan of boiling salted water cook the zucchini, cauliflower, and corn until crisp-tender, about 2 minutes.
Drain and transfer to a platter.
Heat the oil in a medium skillet over medium heat and cook the onion until limp, about 4 minutes.
Add the remaining ingredients, except the cilantro.
Cook, stirring, until the tomato is hot and bubbling, about 2 minutes.
Spoon over the vegetables.
Sprinkle with cilantro.