Preheat oven to 450°F and adjust oven rack to the middle position. Pulse tomatoes and their juice in a food processor until coarsely chopped (6 to 8 pulses).

Heat olive oil in a Dutch oven over medium heat. Add garlic and red pepper flakes, stirring constantly until fragrant (about 2 minutes). Stir in tomatoes and salt, bring to a simmer, and cook until slightly thickened (about 10 minutes).

Trim outer leaves from cauliflower and cut the stem flush with the bottom of the florets. Stir in raisins, olives, and capers, then nestle the cauliflower stem side up into the sauce. Spoon some sauce over the cauliflower, cover, and transfer the pot to the oven. Roast for 30 to 35 minutes, until the cauliflower is just tender.

Remove the pot from the oven and carefully flip the cauliflower stem side down. Spoon more sauce over the cauliflower and scrape down the sides of the pot. Return the pot to the oven uncovered and continue roasting for 10 to 15 minutes, until fully tender.

Remove the pot from the oven. Sprinkle the cauliflower with Parmesan and parsley, and drizzle with extra olive oil. Cut into wedges and serve with the tomato sauce spooned over individual portions.