1. To prepare the dressing, process the ingredients in a blender. Season with salt and pepper.

2. Preheat the broiler. Broil the peppers, turning from time to time, until blackened on all sides. Let cool until handleable. Remove the blackened skin, seeds, and ribs. Cut the peppers into thick strips.

3. Preheat the oven to 375°F (190°C). Place the onions on a rimmed baking sheet, toss with 1 tbsp of the oil, and season with salt and pepper. Roast for 20 minutes. Add the cherry tomatoes, drizzle with 1 tbsp more oil, and the vinegar. Roast for 10 minutes more, until the onions are tender. Let cool.

4. Increase the oven temperature to 425°F (220°C). Heat remaining 4 tbsp oil in a large frying pan over high heat. Add the beef and cook, turning occasionally, about 10 minutes, until browned on all sides. Transfer to a roasting pan. Roast about 20 minutes until a meat thermometer reads 130°F (55°C) for medium-rare meat. Transfer to a carving board. Let cool, and thinly slice the beef.

5. Toss the mesclun with ¼ cup of dressing. Add the beef, red pepper, onions, and cherry tomatoes. Serve with extra dressing on the side.