Cut onions, carrots, and Bulgarian pepper into thin strips. Mushrooms are optional.
Fry the vegetables on medium-high heat for 8 minutes, stirring frequently.
Add minced garlic and parsley, cook for 1 minute, then remove from heat.
Cut potatoes into 0.5 cm slices. Fry on both sides on medium-high heat for 6–8 minutes until golden brown.
Slice the mullet fillets diagonally (at approximately 45 degrees) into thin slices.
Make the sauce: mix cream, minced garlic, soy sauce, parsley, black pepper, coriander, and a raw egg. If using sour cream instead, add honey or sugar to prevent souring.
Layer in a baking dish: fried potatoes on the bottom, pinch of salt, mullet slices, pinch of salt, cooked vegetables, tomato slices, pinch of salt, and a final layer of fried potatoes. Pour sauce over the top.
Bake in an oven preheated to 240°C (464°F). When the sauce starts to boil, sprinkle grated Suluguni cheese over the top. Continue baking until the cheese is melted and lightly browned.