Crumble lye pastry very finely. Wash the thyme and remove the leaves. Wash the lemon and finely grate the peel. Cut lemon into thin slices. Mix the crumbs, thyme, 2 tablespoons of mustard, 2 tablespoons of oil and lemon zest.
Peel and wash the potatoes and cook in salted water for about 20 minutes. Clean and wash the salad. Wash and chop parsley. Wash, quarter, seed and dice tomatoes.
Rinse fish, pat dry and cut into 4 pieces. Season fish with salt and pepper. Line a casserole dish with lemon slices. Place the fish on top. Spread the breadcrumb mixture on the fish and press down lightly. Bake in a preheated oven (electric cooker: 180 °C/circulating air: 160 °C/gas: see manufacturer) for approx. 10 minutes.
Drain the potatoes. Add butter and let it melt. Add parsley and toss everything. Mix vinegar, salt, pepper, 2 tablespoons mustard and honey. Fold in 2 tablespoons of oil. Mix salad, tomatoes and vinaigrette. Arrange everything.