Preheat oven to 425°. Toast sesame seeds in a small dry skillet over medium heat, swirling occasionally, until beginning to brown, about 2 minutes. Transfer to a bowl. Add cumin, poppy, and sunflower seeds to skillet and cook, swirling occasionally, until cumin seeds are fragrant, about 2 minutes. Transfer to bowl with sesame seeds; season with salt and 1/2 teaspoon coriander.

Toss broccoli with oil and remaining 2 teaspoons coriander; season with salt and pepper. Spread in a single layer on a baking sheet and roast, flipping once, until charred in spots and tender but not mushy, about 20 minutes. Let cool 15 minutes. Toss with feta brine.

Arrange broccoli and feta on a platter.  Sprinkle evenly with turmeric and drizzle generously with oil. Top with toasted seeds and serve warm or at room temperature.