I would say both options are correct. However, you may find this explanation helpful:
-to find: infinitive
Both gerunds and infinitives can be used as the subject or the complement of a sentence. However, as subjects or complements, gerunds usually sound more natural in spoken English.
In the following example sentences, gerunds sound more natural and would be more common in everyday English. Infinitives emphasize the possibility or potential for something and sound more philosophical:
Learning is important. normal subject
To learn is important. abstract subject - less common
The most important thing is learning. normal complement
The most important thing is to learn. abstract complement - less common
If this sounds confusing, just remember that 90% of the time, you will use a gerund as the subject or complement of a sentence.
It's all fair and well for an author to propose rules of "abstractness' and "normality" for second-language speakers. Perhaps, this particular grammarian did not have the advantage of accessing GOOGLE in his/her day.
In any case, if one enters the phrase "It is easy to learn" in that most popular of search engines, one receives the following results:
Results 1 - 10 of about 19,700,000 for "It is an easy way to learn". (0.35 seconds)
Similarly, if one enters it "It is an easy way oflearning" , one receives the following results:
Results 1 - 10 of about 19,500,000 for "It is an easy way of learning". (0.16 seconds)
I would say that this is proof positive that the two expressions are both equally common in the everyday usage of Contemporary English.