Hanumān never speaks in the Gītā, but he is there from the first chapter. Arjuna is called kapi-dhvaja, the one whose banner bears Hanumān. He stays on the banner above the chariot for all 700 verses.
Going deeper
The Gītā opens on a battlefield, and Hanumān appears before Arjuna says a word. 1.19 ends the account of the conches: the uproar shakes heaven and earth and breaks the hearts of Dhṛtarāṣṭra's sons. Then 1.20 turns to Arjuna. Seeing Dhṛtarāṣṭra's sons drawn up and the missiles beginning to fly, he lifts his bow, and the verse calls him kapi-dhvaja, the one whose banner crest is Hanumān. 1.21 gives his first words, asking Kṛṣṇa to draw the chariot up between the two armies. So the banner is named at the moment he takes up his bow and just before he speaks. The verse tells you who is on the chariot, and under whose sign, before the teaching has begun. The scene is set in chapter 1, and what the Gītā says about courage gathers related verses.