Have a Salamander (or Mole) Trek Member fall in love with a Human Trek Member.
Recipe:
1. (optional) Create an easy Campaign with "Restart expedition" on-failure.
2. Find an Archipelago map (either normal expedition, or wait for the Story Act)
3. Recruit a Salamander from the leader of the village
4. Return to your ship and dismiss everybody from the trek, with the exception of the Leader and the Salamander
5. Click "Rest" multiple times until the random romance event triggers ("Accept flowers")
6. (optional) Abandon expedition