How to Make It
Preheat the oven to 400°. In a blender, puree the anchovies, garlic, chile, chicken stock, lemon juice, parsley, rosemary and 3 tablespoons of the olive oil until smooth. In a large roasting pan, preferably nonstick, toss the potatoes, onions and fennel with the anchovy puree. Seasons with salt and pepper and spread them in an even layer. Roast for about 35 minutes, stirring twice, or until just tender.
Divide the remaining 1 tablespoon of oil between 2 large nonstick skillets. Season the tuna with salt and pepper, add 4 steaks to each pan and cook over high heat until nicely browned, about 6 minutes. Turn and cook for 1 minute.
Set the tuna steaks, browned side up, on the vegetables and roast for about 6 minutes, or until the tuna is cooked through. Arrange the tuna and vegetables on a large platter and serve.