1. Heat oven to 400 deg.
2. In a blender, puree first eight ingredients but only using 3 T of the olive oil.
3. In a large roasting pan, toss the potatoes and onion with the puree. Season with salt and pepper and spread them into an even layer.
4. Roast for 35 minutes. Stirring twice.
5. In a skillet, add 1 T. oil. Season the tuna with salt and pepper.
6. cook over high heat for about 6 minutes just on one side. then turn and 2 minutes on the other side.
7. Set the tuna steaks on the vegetables and roast for 6 minutes.
8. Serve tuna with vegetables.