Wash the catfish fillet and cut it into 4 equal portions. Season with salt and pepper and let it rest for 10 minutes.
Wash the zucchini, then slice it thinly. Salt it lightly, drizzle with a little olive oil, mix, and let it rest for 10 minutes.
Wash the fresh herbs, dry them, then chop them and place them in a bowl. Grate the cheese and add it to the bowl. Grate the garlic and also add it.
Prepare the herb cheese sauce. Bring the milk to a boil. Get a whisk ready and place all ingredients near the stove, as you will need to work quickly. Once everything is ready, heat the butter in a small saucepan, then add the flour. Lightly toast it, then gradually pour in the hot milk. Whisk until smooth and thickened into a sauce consistency. Season with salt, then add the grated cheese, garlic, and chopped herbs.
Take an oven dish or a high-sided heatproof glass baking dish. Drizzle the bottom with olive oil. Place the fish fillets inside and pour the herb cheese sauce over them. Spread it evenly, then arrange the zucchini slices on top. Cover with aluminum foil.
Bake in a preheated oven at 200°C / 392°F for 30 minutes covered with foil, then another 20 minutes without foil.
Serve with steamed couscous. To prepare it, bring the water to a boil, then add the couscous and salt. Stir, remove from heat, cover, and let it rest for about 10 minutes, or until tender.