Place fennel seeds in a coffee grinder and coarsely grind and place on a large plate. Brush tuna with olive oil and season with salt and pepper to taste. Preheat saute pan or grill pan over high heat until smoking. Dredge one side of the tuna in the fennel seeds. Saute, fennel-side down for 2 to 3 minutes until golden brown, turn over and continue cooking for 1 to 2 minutes for rare doneness.
Saffron-Roasted Red Pepper Sauce:
Heat oil in a medium saute pan over medium heat. Add the onions and garlic and cook until soft. Add the red peppers, vinegar, water and saffron and bring to a simmer. Cook for 15 to 20 minutes. Place in a blender and blend until smooth, season with salt and pepper to taste.
Heat 3 tablespoons of the olive oil in a medium saucepan over medium-high heat. Add the couscous and cook until lightly golden brown. Cover with water and 2 tablespoons of salt. Cook until al dente, drain and place into a large bowl. Heat remaining 3 tablespoons of oil in a large saute pan and saute the vegetables until just cooked through. Add the vegetables and oil to the couscous. Whisk together the soy sauce and harissa and pour over the couscous and mix to combine. Season with salt and pepper to taste.