Season the loach fillets with salt and pepper and turn in the flour. Heat 4 tablespoons of oil in a pan and fry the loach fillets on each side for approx. 4 minutes until golden brown.
Sauté the onion and garlic cloves in the remaining oil. Deglaze with the vegetable stock and lemon juice and let reduce. Season to taste with salt, pepper and sugar. Halve the cherry tomatoes, add them and leave to stand for another 5 minutes.
Pour the sauce on four plates and place a fish fillet on each one.