Toast curry powder, stirring frequently, in a small, dry frying pan over low heat until fragrant, about 1 minute. For the vinaigrette, whisk lime juice, curry powder and salt in a small bowl. Whisk in vegetable oil.
Cook beans in a large saucepan of lightly salted boiling water until crisp-tender, about 3 minutes. Transfer with a slotted spoon to a colander. Rinse under cold running water.
Add cauliflower florets to the boiling water. Cook until crisp-tender, about 4 minutes. Drain in colander. Rinse under cold running water.
Toss beans, cauliflower, corn and vinaigrette in a large bowl. Serve chilled or at room temperature.
Toasting curry powder in a dry frying pan gets rid of the raw taste and boosts the flavour. Other spices, such as cumin and chilli powder, benefit from toasting, too. They can be added to foods that don't require further cooking.