large head of garlic, halved crosswise
extra-virgin olive oil, plus more for brushing
1/2-inch-thick slices of Italian bread or ciabatta, halved lengthwise
small arugula leaves, for garnish
smoked mackerel fillets fillet broken into 6 pieces, about 3/4 pound skin removed and each
small red onion, thinly sliced
medium tomatoes, halved and thinly sliced
1. Preheat the oven to 350°. Set the garlic on a piece of foil, cut sides up. Brush with oil and wrap the garlic in the foil. Bake for 40 minutes, until softened; let cool slightly.
2. Meanwhile, light a grill. Brush the bread slices on 1 side with 2 tablespoons of the oil. Grill over high heat until lightly charred, about 1 minute per side.
3. Squeeze the roasted garlic into a bowl and mash with a fork. Stir in the remaining 2 tablespoons of oil and season with salt.
4. Spread the roasted-garlic puree on the grilled bread and arrange a few arugula leaves on top. Top with the mackerel and onion and tomato slices and serve.