Heat two tablespoons of the oil in a large saucepan and fry the onion and potatoes gently for about 10 minutes, or until the vegetables are softened but not brown.
Add the garlic and cook for a further minute.
Add the stock and season with salt, to taste. Bring the stew to the boil, then reduce the heat, cover and simmer for about 10 minutes or until the potatoes are tender.
Add the broad beans and cook for a further minute. Stir in the chopped spinach and cook for 1-2 minutes, or until the spinach is wilted. Finally, stir in the mint and season with freshly ground black pepper, to taste.
Heat a frying pan until hot, add the remaining olive oil and fry the gurnard fillets, skin side down, for 2-3 minutes, or until just crisp. Flip the fillets over and continue to cook for another two minutes, or until the fish is cooked through.
Remove the gurnard from the pan and set aside to rest for 1-2 minutes.
Meanwhile, heat a separate frying pan and fry the bacon lardons for 2-3 minutes, or until golden-brown and crisp.
To serve, divide the stew between two bowls, top each with two gurnard fillets and sprinkle over the bacon lardons.