Put garlic cloves, cumin seeds, and a pinch of salt in a mortar and pestle and crush until seeds are cracked and garlic is in small, flimsy chunks. If you don't have a mortar and pestle, mince garlic very fine.

Empty fava beans (with liquid) into a medium saucepan and combine with tahini and garlic paste. Cook over medium-high heat, stirring frequently, until liquid retains some brothiness but turns thick and sauce-like, about 5 minutes.

Add lemon juice and salt to taste. Mash one third of the beans with a potato masher to thicken if desired, then serve with toasted pita.