Arrange cauliflower florets in a single layer in a 13 x 9-inch metal baking pan. Drizzle with 1 tablespoon olive oil; sprinkle with black pepper and kosher salt, tossing to combine. Bake at 400° for 40 minutes or until cauliflower is lightly browned.
Heat remaining 2 teaspoons oil in a small skillet over medium heat. Add prosciutto to pan; sauté 10 minutes or until crisp, stirring occasionally. Add garlic to pan; sauté 1 minute. Drain on paper towels.
Combine cauliflower mixture, prosciutto mixture, and vinegar in a large bowl; coarsely mash with a fork. Stir in chopped parsley. Spoon 2 tablespoons cauliflower mixture into each endive leaf. Serve warm or at room temperature.