Heat the oil in a large dutch oven, and add the curry paste and saute over high heat for 1-2 minutes. Add the onions and reduce the heat to medium-high, and cook for another minute or two. Then add the cauliflower, bell pepper, and salt and stir well. Pour in the broth and coconut milk, stir to combine, cover and let the mixture simmer until the cauliflower is soft, about 8-10 minutes. Uncover and add in the shrimp, cook until until shrimp are opaque and cooked through. Serve with topped with cilantro and lime wedges, and with steamed rice or rice noodles if desired.