For the Rioja Red Wine Sauce: Place port, wine, sugar and honey in a medium stainless steel saucepan and cook over high heat until reduced to 1/4 cup, let cool. Place reduced liquid in a blender and with the motor running, add oil until emulsified. Season with lemon juice and salt and pepper to taste.
For the Pearl Onions: Place water, butter and sugar in a medium saucepan and cook until the butter and sugar is melted. Add onions and cook over high heat until the water has evaporated and the onions are cooked through and caramelized. Season with salt and pepper and lemon juice.
For the Tuna: Heat a small saute pan over high heat. Add the fennel seeds and toast for 1 to 2 minutes. Place the seeds in a coffee grinder and grind until coarsely chopped. Season the tuna with salt and pepper to taste on both sides. Dredge 1 side of each fillet in the fennel seeds. Heat the oil in a large saute pan over high heat. Saute the tuna, fennel-side down until golden brown 1 to 2 minutes. Turn the fish over and continue cooking for 1 minute for rare doneness. Drizzle the fish with Rioja sauce and parsley. Serve with caramelized onions and braised fennel.
For the Braised Fennel: Brown fennel in olive oil in medium pan. Deglaze pan with wine and stock. Season with salt and pepper. Cover and braise until tender.