In a small bowl, combine the garlic, half the lemon juice, 120ml oil, parsley or coriander, cumin, salt and pepper.
Make three 3mm slits across the length of each fish or on the skin-side of half of the fillets and spread the mixture over the fish and into the slits.
Arrange the potatoes in a single layer in a large roasting tin and place the fish on top. Scatter the tomatoes, peppers or chillies over the fish and pour the stock or water into one corner of the tin.
Drizzle the remaining oil and lemon juice over the fish, then cover tightly with greaseproof paper and foil and bake for about 15-20 minutes, until the fish is opaque.
Remove the foil and cook for a further 2 minutes, or until the fish flakes easily when pricked with a fork.
Arrange the fish and potatoes on a serving dish and spoon the tin juices over them.