Heat the oil in a large saucepan and gently soften the onion. Once the onion becomes translucent, stir in the garlic and cook for 2-3 minutes.
Add the rice and gently toast it until the outside appears opaque.
Slowly add the stock, stirring regularly until all the stock has been absorbed and the rice is cooked but retains a bite.
Stir in the spinach and continue cooking for 5 minutes, until all the spinach has wilted.
Stir in the parsley, dill, half of the feta and lemon juice, and season to taste.
Serve topped with the remaining feta.