Can a waiter put a note like no onions on a round before sending it to the kitchen?

Yes. On the waiter's phone, press Add to this table, pick the dishes, and use the note box for no onion, less sugar or anything the cook needs to know. The note travels with the round to the kitchen screen and the printed ticket. If the note mentions an allergy, the ticket lifts it into its own warning line above the dishes. That is what tableside ordering is for: the order is taken once, at the table, and never retyped. The Tables, tabs and the kitchen screen tab in the docs covers rounds.