Prep garlic bread: Cut ciabatta crosswise into 1⁄2-inch thick slices. Brush lightly with oil and arrange on a rimmed baking sheet.

Prep ingredients: Chop tomatoes in their can with kitchen shears before straining over a bowl; reserve liquid separately. Finely chop celery. Halve onion, then peel and finely chop. Peel 2 large garlic cloves and finely chop 1, leaving the other clove whole. Pick 1 teaspoon thyme leaves from stems for step 6; reserve remaining sprigs for step 3. Peel potato and cut into 1⁄2-inch pieces.

Sauté aromatics: In a medium pot, heat 2 tablespoons oil over medium-high. Add celery and onion and cook, stirring occasionally, until softened, about 5 minutes. Stir in chopped garlic, half of reserved thyme sprigs (save rest for own use), and a generous pinch salt and pepper, and cook until fragrant, about 1 minute.

Build soup: Add chopped tomatoes and cook until very dry, about 3 minutes. Add 2 cups water, clam broth concentrate, strained tomato liquid, 1⁄4 teaspoon salt, and several grinds of pepper, and bring to a boil. Add potatoes, cover partially, and cook over medium heat until potatoes are just tender when pierced with a knife, 10 -12 minutes.

Make garlic bread: Preheat broiler with top rack 6 inches from heat source. Broil bread, turning once, until golden, 1–2 minutes (watch closely as ovens vary). Halve reserved whole, peeled garlic clove and rub it over cut-sides of toasted bread; sprinkle lightly with salt.

Finish soup & serve: Cut pollock into 1-inch pieces and add to soup. Cover and cook just until fish flakes easily, 2–3 minutes. Remove thyme sprigs and ladle soup into bowls. Sprinkle with reserved thyme leaves and pepper, and drizzle with olive oil. Serve with garlic bread on the side for dipping or crumbling over.