Breadcrumbs, part 1: Preheat broiler. Position the oven rack two rungs from the top. Place torn bread on a rimmed baking sheet in an even layer, then place sheet under the broiler. Cook 4—5 minutes, until bread is dried out and lightly toasted. Remove and set aside.
Cauliflower: With the broiler still on, heat a rimmed baking sheet on the same rack under the broiler. Meanwhile, cut the cauliflower into quarters, then into ¼-inch slices. Break up the larger pieces (don’t worry if smaller pieces fall off). Place the cut cauliflower into a large bowl and drizzle with olive oil. Sprinkle the salt over the bowl from a height of 8—10 inches. Toss cauliflower and place on the pre-heated baking sheet in an even layer. Return the sheet to the broiler and cook 15 minutes, stirring every 5 minutes or so to allow color to develop.
Garlic paste: Smash the garlic clove with the flat side of a knife, then finely chop it. Sprinkle with ½ teaspoon salt and continue chopping. Place the heel of your hand on top of the flat side of the knife and smash the garlic-salt mixture. The mixture will look wet as it releases oils; after a minute, it will become smooth, yielding garlic paste. Put into a small jar and set aside.
Anchovy paste: Just as you did with the garlic, finely chop the anchovies, sprinkle on ½ teaspoon salt, then chop the salt and anchovies together. Again, use the flat side of the knife to smash the mixture into a paste, then add it to the jar along with the garlic paste.
Dressing: To the garlic and anchovy paste, add ¼ cup olive oil, chili flakes, and lemon zest. Cover and shake, about 30 seconds. Taste to adjust seasonings and set aside.
Breadcrumbs, part 2: Place the dried bread between two sheets of parchment paper in an even layer. Using a rolling pin, roll over the top layer of parchment paper and crush the bread to a medium consistency. Add 2 tablespoons olive oil to a medium skillet over medium-low heat. When oil is hot and shimmering, add the breadcrumbs, toss to coat, and toast, 3—4 minutes. Season with ½ teaspoon kosher salt and ¼ teaspoon black pepper.
Assemble: Put the blistered cauliflower in a large bowl. Toss with half of the dressing. (The rest will keep in the covered jar up to a week; use on fish, grilled vegetables, or as the base of a vinaigrette.) Then place the cauliflower back on the baking sheet and put under the broiler for 2—3 minutes. To serve, place the cauliflower on a platter and top with breadcrumbs and parsley.