DM Academy

I'm running a homebrew of Monster Hunter as a first time DM, with sort-of first time players. They treat it like a Disneyland ride where they "go here do X" and so I set them up for the first major boss fight with Teostra (cr13) against their group (lv4) with the inte t that they do 1/4 to 1/2 it's health to drive it away. (I know they can't kill it).

Except rather than fight it they offered to make it a cooked meal, since it can speak draconian and I want them to actually try to roleplay I let it unfold. Except now I have no idea how to proceed. I want this to pan out because it's the first time they've all truly put their heads together and had to figure out how to proceed to actually strategize in the way I see so many players just naturally do in podcasts, but in the spirit of MonHun, the Elder dragons are nearly ageless and you cant...just like reason with them.

I also have no way to set a scene other than pure improvisation for this "city saving cookout" they have to plan. Help?