Preheat oven to 400 degrees F (200 degrees C). Grease a 2-quart baking dish.
Melt coconut oil in a small saucepan. Add panko and toss until toasted, about 5 minutes. Cool to room temperature; stir in pecorino cheese.
Bring a large pot of salted water to a boil. Cut 3 cups of small florets from cauliflower head. Cut remaining cauliflower, including stem, into 2-inch pieces. Boil 2-inch cauliflower pieces and carrots until very tender, 10 to 12 minutes. Strain, reserving water.
Place broth, Gruyere cheese, Neufchatel cheese, Dijon mustard, salt, and hot pepper sauce in the bowl of a food processor. Add cooked cauliflower and carrots; puree until smooth and creamy.
Return water to a boil in a large pot. Add pasta; boil for 3 minutes. Add cauliflower florets; boil for 1 minute more. Strain pasta and cauliflower, return to pot, and stir in cauliflower and cheese mixture. Spread pasta mixture in prepared baking dish; top with shredded Cheddar cheese and the panko mixture.
Bake in preheated oven until golden brown and bubbly, 30 to 35 minutes.