Brown the Italian sausage. Near the end of the browning, add and mix the garlic, then add fennel seeds, and rosemary leaves. Heat for a few moments until aromatic and then reserve (use a slotted spoon and keep the fat in the pan).
Caramelize the onions in the hot sausage fat. About half way through the process add the red pepper. Near the end, combine with the sausage. Heat and mix thoroughly. Reserve.
My Italian red sauce is posted elsewhere. Briefly: Caramelize two diced sweet onions with a diced red pepper. Add these to a food processor with a large can of DOP San Marzano tomatoes, a roasted red pepper, a can of tomato paste, EVOO, herbs and spices to preference. Process together and simmer on low for an hour.
Cut the stem from a large head of cauliflower and remove the leaves. Slice as best as you can into 5 ca. 1-inch slices. I can usually get 3 full slices to hang together and then the remaining pieces just need to be collected.
The slices and pieces are laid out on a baking pan covered with oiled parchment, then sprayed with oil and dusted with ground black pepper. Roast at 450 F for 15-20 minutes on one side. Use a large spatula and turn over all of the pieces, spray with oil and roast another 15-20 minutes, until tender and golden brown. Remove and reduce the heat to 350 F.
Carefully remove the cauliflower to oven-save serving dishes. Coat the cauliflower with tomato sauce.
Place 2-2.5 pieces of mozzarella on each one.
Top with a generous portion of the sausage mixture. Bake at 350 F for 15-20 minutes until the cheese is melted, bubbly and a little browned. Top with some shredded parmesan.