Prepare the tomatoes and bell peppers, working over a bowl to catch all the juices. Cut or tear the peppers into long strips. Strain all the juices into a large non-reactive saucepan. Add the chili. Bring to a boil over high heat, reduce the heat to medium, and simmer until the juices reduce to a heavy syrup and the chili is very soft, about 10 minutes. Scoop out the chili, seed if desired, and mince. Add the peppers and tomatoes to the saucepan and bring to a boil. Lower the heat to medium and simmer for 20 minutes. Stir in the chili and salt and pepper to taste. Keep warm or let cool to room temperature.
Prepare the grill and let it burn down to medium coals. Season the flank steak with salt, pepper, 1 tsp. of the oregano, and brush with 1 Tbs. of the olive oil. Grill, turning once, until done to your taste, about 10 minutes for rare meat. Transfer to a cutting board, drizzle with another 1 Tbs. of olive oil, and crumble the remaining 1/2-tsp. oregano over the top. Let rest for about 5 minutes.
Meanwhile, brush the bread on both sides with olive oil and season with salt and pepper. Grill the bread on both sides until brown and crunchy on the outside but still soft within. Carve the meat on the diagonal into thin slices and arrange on a platter or plates. Top each slice of grilled bread with about 1/4-cup of the roasted peppers in sauce and arrange next to the meat. (Reserve any remaining peppers for another use.)
Gather all the meat juices (make an effort to scrape the meat juices off the carving board, too) into a small bowl and whisk in the vinegar and the remaining 1 Tbs. olive oil. Drizzle over each portion. Serve immediately.
Courtesy Michael Chiarello. Copyright NapaStyle, Inc. 2001 by M. Chiarello, D. Shalleck