In a large skillet over medium heat, add olive oil and sauté onion, garlic, and ginger for about 3 minutes. Add curry powder, cumin, and mustard seeds and sauté for an additional 3 minutes, until fragrant.
Add cauliflower and lime juice and stir-fry on medium-high heat for about 5 minutes. Reduce heat, add coconut milk and broth or water, cover partially, and simmer on low heat for about 5 more minutes, until cauliflower is crisp-tender. Add sea salt to taste, if desired.