Preheat the oven to 400°F (200°C). Line a baking sheet with parchment paper and lightly brush with olive oil.
In a food processor, add the drained chickpeas, 1/2 medium onion, 3 garlic cloves, and 1/2 cup parsley. Pulse until roughly combined but still retaining some texture.
Add the ground cumin, ground coriander, baking powder, chickpea flour, salt, and black pepper. Pulse a few more times until the mixture forms a slightly coarse, bindable paste.
Using your hands, form the mixture into small patties (about 6-8 patties for the full recipe) and place them on the prepared baking sheet.
Lightly brush the tops of the patties with olive oil. Bake for 20-25 minutes, turning once halfway through, until the falafel are golden and crispy on the edges.
While the falafel bakes, prepare the lemon-garlic tahini sauce. In a small bowl, whisk together tahini, lemon juice, 1 minced garlic clove, and water until smooth and slightly diluted.
For a cooling contrast, stir the nonfat Greek yogurt in a separate bowl. You can add a pinch of salt and extra lemon juice if desired.
To serve, plate 3-4 falafel patties per serving and drizzle with the lemon-garlic tahini sauce. Add a dollop of Greek yogurt on the side or on top, and enjoy your balanced, protein-rich meal.