If I remember correctly, I think there's a way to send a auto-fill component, which when clicked puts a command into the chat window. How do I send this type of ChatComponent?

you need add a Style to a Component and the a ClickEvent, e.g:

Component component = new TextComponent("").withStyle((style) -> {
	return style.withClickEvent(new ClickEvent(ClickEvent.Action.RUN_COMMAND, "command"));
});

 

Thanks!