Rinse cauliflower; cut into quarters. Cut off and discard leaves and cores; cut quarters into 1/4- to 1/2-inch-thick slices.
In a 12- by 17-inch baking pan, mix cauliflower with olive oil and 1/4 teaspoon salt. Spoon half the mixture into another 12- by 17-inch pan and spread mixture in both pans level.
Roast in a 450° regular or convection oven until cauliflower is browned on the edges and tender when pierced, 15 to 20 minutes.
Meanwhile, toast bread slices. Rub one side of each with garlic clove; discard any remaining garlic. Let bread cool, then tear into 1-inch chunks. In a food processor or blender, whirl to coarse crumbs.
In a large bowl, mash anchovies with lemon juice to a coarse paste. Add cauliflower, parsley, capers, hot chili flakes, and bread crumbs, and mix. Add salt to taste.