Preheat the oven to 425 degrees F. Lightly grease a sheet pan with oil.
In a large bowl, stir 1 tablespoon oil, harissa, cumin, 1/2 teaspoon kosher salt and 1/4 teaspoon black pepper.
Add the cauliflower to the harissa marinade. Stir it around, so it is coated in the mixture.
Spread the cauliflower across the baking sheet in a single layer. Roast until it is tender and browned at the the edges, flipping halfway through roasting, about 20-25 minutes.
While the cauliflower roasts, make the herb oil. Combine the parsley leaves, cilantro leaves, lemon juice, 1/3 cup oil, 1/2 teaspoon kosher salt and 1/4 teaspoon black pepper in a food processor or blender. Process until the herbs are finely chopped, and the oil is bright green.
For the couscous, combine the couscous grains and boiling water in a large bowl. Cover and let sit for 5 minutes. Use a fork to comb through the couscous, breaking up any clumps.
Stir the herb oil into the couscous.
Then fold in the roasted cauliflower. Top with chopped herbs before serving.