1 large cauliflower head
1/2 cup pitted, oil-packed, black olives, finely chopped
3 sun-dried tomatoes, thinly sliced and soaked for 4 minutes in warm water
31/2 tablespoons olive oil, divided, plus more to taste
2 tablespoons chopped, fresh, flat-leaf parsley
1 teaspoon fresh lemon juice
Kosher salt and freshly ground black pepper, to taste
3 garlic cloves, peeled
2 plum tomatoes, cored and quartered
Remove leaves and trim stem end of the cauliflower, leaving core intact. Place cauliflower, core-side down, on a work surface. Using a large knife, slice cauliflower into four 1/2-inch "steaks" from center of cauliflower (some florets will break loose; reserve). Finely chop enough loose florets to measure 1/2 cup.
Transfer chopped florets to a small bowl and mix with the olives, sun-dried tomatoes, 1 tablespoon of the olive oil, the parsley and lemon juice. Season relish with the salt and pepper.
Heat oven to 400 F. Heat 1 tablespoon olive oil in a large, heavy, ovenproof skillet over medium-high heat. Working in 2 batches, cook cauliflower steaks until golden-brown, for about 2 to 4 minutes per side, adding 1 tablespoon oil to pan between batches.
Transfer steaks to a large, rimmed baking sheet. Reserve skillet. Roast cauliflower until tender, for about 15 to 18 minutes, turning halfway through.
Return skillet to medium-high heat and add the garlic cloves and tomatoes, 1 cut side down. Cook until tomatoes are browned; turn tomatoes over and transfer skillet to oven with cauliflower. Roast garlic and tomatoes until tender, for about 12 minutes.
Transfer garlic, tomatoes, and remaining oil to a blender; puree until smooth. Season with salt and pepper. Divide tomato sauce among plates. Place 1 cauliflower steak on each plate; spoon relish over.
Serve warm or at room temperature.
Makes 2 to 4 servings.