Combine the coconut milk, yellow curry paste, and rice vinegar in a small blender. Blend until completely smooth. Set aside until ready to use.
Add the oil, yellow onion, bell pepper, and cauliflower to a large non-stick skillet or wok. Cover, and heat to medium-high. Cook, stirring occasionally, for 8 to 10 minutes. Remove the cover and continue cooking, stirring occasionally, until onion and cauliflower begin to brown, about 8 minutes.
Pour the coconut milk-curry mixture into the skillet and continue cooking until much of the liquid has evaporated, about 3 minutes.