Make the pickled onions. Pack the onion slices, red wine vinegar, sugar, and salt in a 16-ounce jar or similar. Add 1 cup of boiling water and stir gently until the sugar and salt dissolve. Let cool slightly, then cover and refrigerate for at least 2 hours and up to 2 weeks. Roast the cauliflower. Set the oven to 400°F. In a small bowl, combine the spices, sugar, and salt with the olive oil and mix well. Place the cauliflower on a sheet pan and pour the spice mixture over the florets. Rub the mixture all over the cauliflower, then arrange in a flat layer. Roast, flipping every 15 to 20 minutes, until the cauliflower is golden brown, crispy, and fork-tender—35 to 45 minutes. Toast the nuts. Place a small skillet over medium-high heat. Add the pine nuts and stir occasionally for 2 to 3 minutes or until the nuts are fragrant and mostly golden brown. Set aside to cool. To make the salted yogurt, add the yogurt, olive oil, and salt to a medium bowl and mix well to combine. To serve, spread the yogurt mixture on large plate and arrange the cauliflower on top of it. Scatter with pickled onions, mint, and pine nuts as desired. Serve with warm flatbreads or rice.