Tear off any broccoli leaves and trim the bottoms of the stems. Cut the florets just above where they join the large stem, and then cut each floret through its stem (but not the buds) so that each piece is about 1/4 inch thick at the stem end. Using a vegetable peeler or paring knife, peel the tough outer skin from the large stem, removing as little flesh as possible. Cut the stem into baton-shaped pieces about 1/4 inch wide and 2 inches long. Cut the core out of the cauliflower to separate the florets, and then cut each floret through its stem so that it’s about 1/4 inch thick at the stem end. Discard the core.
Set a 12-inch skillet over high heat. Pour in 3 Tbs. of the olive oil and then add the broccoli florets and stem pieces. Season with salt and carefully add 3/4 cup water. Reduce the heat to medium high and cook, stirring occasionally, until the broccoli is tender and browned in spots, 8 to 10 min. (If the pan begins to scorch before the broccoli is cooked, add another 1 Tbs. olive oil and reduce the heat a little. If the pan does scorch, rinse and dry the pan before cooking the cauliflower.) Transfer the broccoli to a large bowl. Wipe out the pan and cook the cauliflower the same way. Add the cooked cauliflower to the bowl with the broccoli.
Wipe out the pan (if it’s scorched, rinse and dry it) and return it to the stovetop over medium heat. Add 2 Tbs. olive oil, the onion, chile flakes, and saffron; season with salt. Sauté, stirring frequently, until the onion is golden brown and tender, about 8 minutes. Push the onion to one side and add 1 Tbs. olive oil and the yellow and brown or black mustard seeds. Let the seeds sizzle for 1 min. and then add the garlic and ginger. Cook, stirring, for 1 min. more—be careful not to let them burn.
Return the broccoli and cauliflower to the pan, stir to combine, and cook until hot, about 2 min. Taste and add salt if necessary. Transfer to a platter, sprinkle the cilantro on top, and serve the lime wedges on the side.