If you are planning to roast your red pepper, rather than use store bought, place your pepper under broiler to blacken. See red pepper method below.
Preheat a large nonstick skillet over high heat. Pat tuna steaks dry and season with a little coarse salt. Drizzle extra virgin olive oil over tuna and lightly coat steaks on both sides. Coat 1 side of the steaks with a generous amount of coarse ground black pepper. When the pan is very hot, add steaks, peppered side down. Sear and brown steaks 2 minutes, then turn, and immediately reduce heat to medium. Loosely cover pan with aluminum foil tent and allow steaks to cook 5 minutes for rare, 7 minutes for medium. Steaks should be firm, but have a little give and some pink should remain at the center.
In a second skillet over moderate heat, coat pan with olive oil, add garlic and onion, and saute 3 minutes to soften onion bits. Add beans and chopped roasted red pepper to the pan. Heat beans through, 2 to 3 minutes. Stir in rosemary and parsley and season beans with salt and pepper.
Combine escarole and radicchio in shallow dish. Coat greens with lemon juice, then a drizzle of oil. Season salad with coarse salt and toss well.
To serve, pile a serving of beans on a dinner plate and top with tuna steak. Serve salad greens along side beans and fish. You can also serve this with sliced bread that has been toasted and then rubbed with half a garlic clove.
To roast red peppers: Preheat broiler to high. Split and seed pepper and place skin side up close to hot broiler. Blacken skins of pepper. Transfer pepper to brown paper bag and seal. Let pepper cool to handle. Peel charred skins away from pepper flesh.