Heat the oven to 400.
Cut the beef into 4 even slices. Heat 1 Tb. of the oil in a large skillet. Sauté the onions over medium heat 5 minutes, season with salt and pepper. Lower heat and cook 30 minutes, until caramel colored, stirring occasionally. Stir in tomatoes and arugula, set aside.
Heat a medium skillet and add the remaining tablespoon olive oil over medium- high heat. Sear the meat for 3 to 4 minutes per side seasoning with salt and pepper as you go. Transfer to a baking sheet.
Place the beef in the oven for 5 to 10 minutes depending on desired doneness.
Melt the butter in the same skillet and sauté the shallots until translucent about 2 minutes. Season with salt and pepper. Add the brandy and reduce to a few tablespoons over high heat. Add the stock and bring to a boil. Reduce by half and then taste for seasoning. Remove from heat.
Mound a serving plate with the onion-arugula mixture. Place the meat on top. Ladle sauce over meat and garnish with chopped parsley.