Place a large pot of water over medium heat and cover to bring pot to boil. Peel off 10-12 leaves from the head of cabbage and place in water for about 3-4 minutes, until soft and pliable. Place the blanched cabbage leaves in a colander to drain off excess water and cool to touch.
Grease a 8×8 baking dish. In a large bowl, mix together cauliflower, pepper, onion, garlic, and italian sausage until combine. Scoop about 1/4-1/3 cup of the mixture into each of the cabbage leaves. Fold in two sides, then roll (like a burrito). Place fold side down in a baking sheet. Repeat with the rest of the meat and leaves. If you have leftover meat, press it into the crevices between the cabbage rolls.
To make pizza sauce, heat the olive oil in a medium sauté pan over medium heat. Add the onion and garlic and cook until the onion is soft and translucent, about 5 minutes. Add the sun-dried tomatoes and sauté for about 2 minutes, until fragrant. Add the remaining ingredients and bring to a low boil. Reduce the heat to low and allow to thicken for about 10 minutes.
Once thickened, pour pizza sauce on top of cabbage rolls. Cover with foil and bake for 1 hour and 15 minutes.