And, O Bhima, having felt a human being by coming in contact with thee, I have been put in mind of that son of Raghu, who was Vishnu himself under the name of Rama, and who delighted the heart of the world; and who was as the sun in regard to the lotus face of Sita, and also to that darkness—Ravana. Therefore, O heroic son of Kunti, let not thy meeting with me be fruitless. Do thou with fraternal feeling ask of me a boon, O Bharata.

In plain words: Hanuman says touching a human again reminded him of Rama, who was the god Vishnu in human form and brought joy to the world and to Sita. So he asks Bhima, as a brother, to ask him for a gift so their meeting is not wasted.