By not boiling the vegetables, you retain all the flavor and nutrients that would have otherwise gone down the drain.
Heat oil in a large pot over medium-high heat. Add cauliflower, broccoli, and salt. Cover, and cook, stirring occasionally, until partially tender, about 8 minutes. Add 3/4 cup water, cover, and simmer over medium-high heat until tender and water has mostly evaporated, about 5 minutes. Mash with a potato masher. Season with pepper.