Preheat the grill to high. Place the tomatoes, cut-sides up, on a heatproof dish. Sprinkle generously with freshly ground black pepper and trickle over the oil. Grill for 4–5 minutes or until browned on top but still firm. Turn off the heat and leave under the grill to keep warm.
Meanwhile, cook the linguine in a large pan of lightly salted boiling water for 10 minutes, or according to the pack instructions, until tender but still firm.
Combine the chilli, cucumber, lemon zest, fennel and chives in a large serving bowl. Add the crab meat and mix lightly.
Drain the cooked pasta, add to the crab mixture and toss together. Add the tomatoes and their juices together with the rocket and mix lightly, taking care not to break up the tomatoes. Serve at once, with lemon wedges to squeeze over the top.
Add flaked smoked mackerel fillets, smoked salmon pieces or cooked, peeled prawns instead of the crab meat. * If fresh crab is unavailable, substitute 2 x 150g cans of crab meat, drained. * Add another red chilli for an extra kick.