Heat the oil in a large frying pan over medium heat until shimmering. Add the onion and 1 teaspoon of the salt and cook, stirring occasionally, until softened, about 6 minutes. Add the garlic and cook until fragrant, about 1 minute.
Add the curry paste, stirring to coat the onions, and cook until fragrant, about 1 minute. Add the coconut milk, water, soy sauce, and remaining 1/2 teaspoon of salt, stir to combine, and bring to a lively simmer.
Add the cauliflower, chickpeas, and green beans and stir to combine. Reduce the heat to medium low, cover with a tightfitting lid, and simmer, stirring occasionally, until the cauliflower is just tender, about 8 to 10 minutes. Remove from the heat and stir in the basil leaves and lime juice. Taste and season with more salt as needed. Serve with steamed rice.