What have you eaten today?
CORRECT - unfinished time -- I may even eat more, who knows.
I noticed a window was broken and the door was open. Someone broke in.
X - "...someone had broken in" - this happened before you noticed the door was open.
You look tired. What did you do?
X - What have you been doing? -- We are interested in the action that caused the result, not if it was completed.