Place a dry, medium saucepan over medium heat. Add cumin seeds and toast 60–90 seconds, swirling, until very fragrant. Transfer to a mortar; add garlic and crush to a coarse paste (or grind seeds and mince garlic).
Return the saucepan to medium heat. Add the onion and the garlic–cumin paste. Sauté 2–3 minutes, stirring; if it sticks, deglaze with 1 tablespoon water.
Add the rinsed fava beans and diced tomato. Stir and cook 5 minutes to heat through.
Reduce heat to low. Mash about one-third of the beans in the pot to create a creamy base, leaving the rest whole.
Off heat, stir in tahini, lemon juice, parsley, black pepper, and red pepper flakes (if using). If too thick, stir in warm water/broth 1–2 tablespoons at a time until creamy and spoonable. Season with the sea salt and adjust lemon or salt to taste.
Divide among six bowls. Make a small well, drizzle about 1/2 tablespoon olive oil per serving, garnish with parsley, and serve immediately.