That is going to depend on the age of the rabbit and whether it is already used to eating greens and/or grass.
Fresh grass, if that is new for a rabbit, is treated like any other new green. Any new green should be slowly introduced to a rabbit over several days to check for tolerance. Only one type of green should be introduced at a time.
Spinach is high in oxolates and is not on the "safe for every day" list. Kale and romaine may or may not be tolerated for everyday -- it depends on the individual rabbit.
Take a click here to see the list of what greens are safe for every day, which should only be offered occasionally, and how to safely introduce them.
Once a rabbit has been safely introduced to greens, they generally are fine with 2-4 cups per day.