Heat extra-virgin olive oil in a medium skillet over medium-low to medium heat, then add onions and roasted peppers, season with salt and pepper and cook gently until soft but not caramelized, 12 to 15 minutes. Stir in parsley.
Heat a large skillet or a cast iron griddle to high.
Toast the bread under broiler and reserve.
Melt butter in a small saucepan over low heat, add garlic. Remove pan from the heat and set aside until the steaks are cooked.
Season 1 side of the steaks with salt and pepper and place seasoned side down in the hot skillet or griddle.. Cook 3 minutes until the meat can be moved easily. Season the reverse side of meat. Flip steaks, reduce heat to medium and cook 6 to 7 minutes for medium rare, 8 to 10 for just pink. Remove meat and let rest a few minutes. Slice steaks 1/4-inch thick against the grain. Pile onions over toast, top with sliced steak, and spoon garlic butter down over the top of each portion.