A flexible menu function in python
You have an actual error in your code:

$ python test.py 
Traceback (most recent call last):
  File "test.py", line 2, in &lt;module&gt;
    ('Order Pizza', order_pizza),
NameError: name 'order_pizza' is not defined


You need to define menu_entries after creating the things it refers to.

Some notes:


All Python code could benefit from being run through at least one linter such as flake8 or pycodestyle. Nothing springs out at me except possibly the indentation of menu_entries, but it's worth a check.
Generally, names don't need to repeat anything which is understood from context. So def menu(menu_title, menu_entries): could be easier written as def menu(title, entries):
You always add one to mpoint - a cleaner solution would be to mpoint = 1 and continue from there. If mpoint was used for indexing into an array that would be different, but it's really only for presentation.
When reading the code top to bottom I should be able to understand what a name means the first time I encounter it. mpoint should be renamed to what it is (maybe menu_index?).
For consistency (and to write more idiomatic code) the strings in all your print statements should be formatted.
This is a prime example for code which could be made object oriented - obvious classes include Menu, MenuEntry and Order.
Setting task = None and then checking if it's None to check whether you should continue is redundant - you can just continue immediately.
size is unused in order_pizza, so it should be removed.