can/could

I'd use "could." You aren't boasting about how many plates you can eat, you're describing the level of your current craving.

I'd also phrase the first sentence: "I really have a craving for spaghetti." You don't need to use the word "now" to show this is a current condition.

In the context of that sentence, use "could."

It means that I am so hungry that if given the chance, I would be able to (could) eat three plates of food with no problem.

Is this a sneaky prescription, Tico? Is there something wrong with,

"I've really got ..." ?

You don't need to use 'now' but it does add some emphasis, doncha think?

=============

I've really got a craving for spaghetti now. I can / could eat three plates in five minutes!

Both gentlemen envision what is likely the more probable situation, YL, hence their suggestions of 'could'. Sully showed how it is normally an unreal conditional, which causes ENLs to use unreal conditional type modals.

If this was at an "all you can eat" spaghetti dinner, or another similar situation, then 'can' becomes a definite possibility.

There's a common idiom used to express great hunger,

I could eat a horse.

In it you see the unreal conditional sense.