1. Heat olive oil in a large pot over medium heat. Add onion; saute 5 minutes, until softened. Stir in garlic and cook 2 minutes. Add cooked cauliflower, chicken broth and 1 cup water. Increase heat and bring to a boil. Cover, reduce heat to a low simmer and cook 10 minutes. Turn off heat. Carefully transfer to a blender and process until smooth. Return to pot and stir in 1 tsp of the lemon juice. Cover and set aside.
2. Heat canola oil in a 10-inch cast-iron skillet over mediumhigh heat. Season steak with 1/4 tsp of the salt and the pepper. Add steak and cook 3 minutes. Flip and cook 2 to 3 more minutes, until mediumrare. Let rest 5 minutes.
3. Toss arugula with parsley, remaining 2 tsp lemon juice and remaining 1/8 tsp salt. Slice steak and serve family-style over arugula. Serve with soup.