Preheat oven to 425°F. Line a rimmed baking sheet with parchment paper or lightly oil.
Place cauliflower florets, sweet potato cubes, and onion in a large bowl. Drizzle the olive oil over the veggies. Use your hands to toss the veggies with the oil until they are well-coated. Sprinkle the za'atar over the veggies and season well with salt and pepper. Gently toss to coat with the spice mixture.
Transfer the veggies to the prepared baking sheet and arrange in a single, even layer. Roast for 20-25 minutes, or until all of the veggies are tender-crisp.
Meanwhile, prepare the Dried Cranberry Gremolata. Combine citrus juices and zest in a medium bowl and stir in olive oil. Set aside.
In another bowl, combine the dried cranberries, pistachios, herbs, and garlic. Pour the sauce over the top and stir well. Season with sea salt and black pepper, to taste. Cover and refrigerate until ready to use.
To serve, divide the cooked grains between four shallow serving bowls. Top with the roasted veggies and a big spoonful of the Dried Cranberry Gremolata. Garnish with a few more fresh herbs. Serve immediately.