Fill a large, wide saute pan 3/4 full with water, add the lemon juice, and bring to a boil. Blanch tuna in the boiling water for about 4 to 5 minutes. Drain and place tuna on a cutting board. Make small slits in the tuna and push the anchovy strips into them.
Heat the olive oil over medium heat in a large heavy saute pan. Once oil begins to shimmer, add the onions and carrots and saute for 5 minutes. Add the tuna, cover, and cook over low heat for about 10 minutes.
Add the garlic, lettuce and sorrel (if using). Season to taste with salt and pepper. Cover pan again and continue to cook over low heat for 10 minutes. The lettuce should exude some water, but check the veggies periodically to make sure they aren't sticking.
Once the lettuce water has been absorbed, add the wine. Cover and simmer over low heat until the fish is done, basting occasionally. This should take about 15 more minutes.
Carefully remove the tuna from the pan with a large spatula and place on a warmed serving platter. Place the cooked veggies around the tuna and serve immediately.