Place the cooked lentils in a small bowl and mash gently with the back of a spoon — it should be mostly smooth, but with some bigger pieces of lentils for texture. Heat the olive oil in a medium sauté pan. Add the onion and garlic and cook until just soft — about 3 minutes. Remove from the pan, leaving any remaining oil behind. Add the onion, garlic, lemon zest, spices, flour, and egg to the lentils. Mix to combine. Form into 8 balls, then flatten them slightly between your hands. Fry in remaining oil until golden brown and crispy — one and half to two minutes on each side.