Bring 2 quarts of water to a boil in a large saucepan. Add the cauliflower and salt and cook until the florets just begin to soften, about 3 minutes. Drain well and transfer to a paper towel–lined baking sheet to dry and cool.

Combine the hot water and saffron in a small bowl and set aside to steep. Heat the oil and garlic in a small saucepan over medium-low heat until the garlic is fragrant and starting to sizzle, 4 to 6 minutes—keep the heat low so the garlic does not brown.

Stir the sugar, paprika, and rosemary into the garlic oil and cook until fragrant. Remove from the heat and stir in the saffron water, vinegar, salt, and pepper.

Combine the blanched cauliflower, chickpeas, and lemon slices in a large bowl. Pour the warm marinade over the mixture and toss to coat. Transfer everything to a gallon-size zipper-lock bag and refrigerate for at least 4 hours or up to 3 days, flipping the bag occasionally to redistribute the flavors.

Transfer the cauliflower and chickpeas to a serving bowl using a slotted spoon, leaving the excess liquid behind. Garnish with parsley and serve cold or at room temperature.