Bring a large pot of salted water to a boil. Add the spaghetti and cook until al dente, then drain.
Place a large skillet over medium-high heat and coat the pan with oil. Add the onions and cook until translucent, about 5 minutes. Add the garlic and cook for 1 minute. Add the cauliflower, 1 tablespoon salt and enough milk to partially submerge the florets. Increase the heat to high, and simmer until the cauliflower is very tender, about 15 minutes.
Very carefully transfer the cooked cauliflower mixture to a blender and blend until smooth.
Rinse the pan clean and place over medium heat. Return the blended sauce to the pan and add more milk if the sauce is too thick. Remove the pan from the heat and add the cheese, parsley, lemon juice and lemon zest. Add the cooked spaghetti to the sauce and toss to coat. Keep covered until ready to serve.
Heat a large nonstick pan over medium-high heat. Coat the pan with olive oil, add the shrimp and cook until pink and just cooked through, about 4 minutes. Season with salt and pepper.
Top the pasta with the shrimp and serve with lemon wedges, parsley and cheese.
A viewer or guest of the show, who may not be a professional cook, provided this recipe. It has not been tested for home use.
When blending hot liquid, first let it cool for five minutes or so, then transfer it to a blender, filling only halfway. Put the lid on, leaving one corner open. Cover the lid with a kitchen towel to catch splatters, and pulse until smooth.