To prepare the sauce, quarter the tomatoes, scoop out seeds, then finely dice flesh and put into a small bowl. Finely chop the shallot and crush the garlic, add to tomatoes with the lemon zest and juice, chpd herbs and olive oil. Season to taste. Cover and leave the flavours to infuse.
To cook the fish, heat olive oil and butter in a heavy based frying pan. Rinse the cod fillets and pat dry with kitchen roll. Season fillets to taste. Cook over a high heat for 2-3 min on each side, until just cooked through.
To serve, gently warm the sauce in a small pan and drizzle some over each serving plate. Top with cooked cod fillet.