In the theory of numbers we can choose to have our visual attention directed to one item. It can be a single vegetable. Broccoli for example. Single items may be counted as "single focus" even when there are decorative items in it.
This is true for a dish or for a meal. In a meal the example is single focus items look like stewform, or pizza, or casserole, pot pies etc. But the goal for a single focus meal is to have the main plate - with all three primary elements and a sauce- be in one dish.