I think because verb~nikui behaves like an adjective that modifies the object of the verb, it changes the particle that is used.
So although you would say …ご飯
を食べるのは/が難しいです
using ~nikui it would be …ご飯
は/が食べにくいです。
I'm not sure if you could say ご飯
を食べにくい... as gohan is no longer the direct
object (
を) of a nominalized sentence clause, but is the
subject (
は/
が) of the ~nikui-modified adjectival verb (hope that makes sense, not sure if that's the right word for it).
~~
@musicisgood, the subject of the thread and your chosen example are different, as explained by
@Majestic in
post #3, where he gives you examples of using the ~yasui structure to express your example sentence of "Cooking for me is easy to do/handle."
I think the ~yasui structure here is useful more when talking about a particular dish or situation where it's particularly or comparably easier to cook or make something. The subject of the sentence is the object of the verb, so 料理しやすい is more about the dish being easy to make for whatever reason, rather than it being easy for you in particular.
Other ways you could express this idea, where you are the subject of the sentence:
料理はぼくの得意です or simply 料理は得意です > cooking is my specialty/strong suit
(ぼくは) 料理 (をするの) が上手です > (I am) good/skilled at cooking
(ぼくには) 料理が簡単にできます > (To me) cooking is easy/simple to do
Key vocab:
[TABLE=full]
[TR]
[TD]ご飯[/TD]
[TD]ごはん[/TD]
[TD]gohan - rice/food[/TD]
[/TR]
[TR]
[TD]料理[/TD]
[TD]りょうり[/TD]
[TD]ryouri - cooking[/TD]
[/TR]
[TR]
[TD]難しい[/TD]
[TD]むずかしい[/TD]
[TD]muzukashii - difficult[/TD]
[/TR]
[TR]
[TD]得意[/TD]
[TD]とくい[/TD]
[TD]tokui - specialty[/TD]
[/TR]
[TR]
[TD]上手[/TD]
[TD]じょうず[/TD]
[TD]jouzu - skilled[/TD]
[/TR]
[TR]
[TD]簡単[/TD]
[TD]かんたん[/TD]
[TD]kantan - simple[/TD]
[/TR]
[/TABLE]