[rightwingcrazy]

The problem would be growing the plants in the near-vacuum at the Martian surface. Lichen might survive. Where’s my million?

[BitWielder1]

... growing the plants in the near-vacuum at the Martian surface.

You would have to compress the air until the plants can survive in it.
Everything living on Mars will need airtight housing for the next several centuries at least.
There is plenty of sunlight since the atmosphere is so thin, outside the greenhouse.
If you need even more sunlight, use mirrors.