Preheat oven to 425 degrees F. Line a baking sheet with foil; set aside. Cut sweet peppers in half lengthwise; remove stems, seeds, and membranes. Place pepper halves, cut sides down, on prepared baking sheet. Roast for 20 to 25 minutes or until charred and very tender. Bring foil up around peppers and fold edges to enclose. Let stand about 15 minutes or until cool enough to handle. Using a sharp knife, loosen edges of the skins; gently pull off the skins in strips and discard. Cut peppers into strips; set aside.
In a medium saucepan heat the 1 1/2 teaspoons olive oil over medium-high heat. Add pancetta; cook until browned, stirring frequently. Add onion and garlic; cook and stir over medium heat for 3 minutes. Remove from heat. Add spinach, cheese, currants, pine nuts, 1/4 teaspoon of the salt, and 1/4 teaspoon of the black pepper. Set aside.
Place flank steak between two pieces of plastic wrap. Using the flat side of a meat mallet, pound lightly until 1/2 inch thick. Remove top piece of plastic wrap. Sprinkle steak with the remaining 1/2 teaspoon salt and the remaining 1/4 teaspoon black pepper.
Arrange sweet pepper strips lengthwise down the center of the flank steak, leaving 3 to 4 inches uncovered on both sides. Spoon spinach mixture evenly over the pepper strips.
Starting with a long side, use bottom plastic wrap to guide flank steak over and around filling, making a long roll. Tie roll at 1 1/2-inch intervals with 100 percent cotton kitchen string. Tuck in the ends of the roll; using a long piece of string, tie roll lengthwise. (To serve today, omit Step 6 and continue as directed in Steps 7 through 9.)
Wrap meat roll in plastic wrap. Chill for up to 2 days.
Preheat oven to 350 degrees F. Unwrap meat roll. In an extra-large oven-going skillet or braising pan heat the 2 tablespoons olive oil over medium-high heat. Add meat roll; cook until browned on all sides, turning frequently.
In a small saucepan combine marinara sauce and wine. Cook over low heat just until boiling. Pour sauce mixture over meat roll in skillet. Cover tightly. Bake about 1 1/2 hours or until meat is fork-tender.
Remove meat from skillet; remove strings and cut meat into 1-inch slices. Serve with the remaining sauce mixture in skillet.