...means: 80 grams of scallops, 100 grams of rice, 80 grams of mushrooms and 22 grams of sweet pepper, and the whole dish costs 178грн.
That's right. 178 is a price of the whole portion. Why did you feel that you need to multiply the price by 4?

If something is sold by weight, then the price for 100 gr (or 100 ml for drinks) is given, and it's usually indicated in some way in the menu. I noticed at least one such dish here: a fried carp at the bottom of the same page. Since carps can be of different size they prefer to charge 25 grivnas for every 100 grams instead of setting a price for a portion. The menu clearly states "sold by weigh" in Ukrainian (literally "weight-y dish"), while the English translation does not seem all that clear.. "dish gravimetric"??? I wonder if people get confused or is it a common way to say it.