Greek Style Beef Meatballs

500g lean beef mince

1 small red onion, finely diced

1 1/2 tbsp oregano leaves, finely chopped + extra sprigs, to serve

Zest of 1 lemon + extra wedges, to serve

1 tbsp olive oil

400g tomato passata

1/2 cup (125ml) salt-reduced beef stock
2 zucchini, cut into 1cm dice

2 celery stalks, cut into 1cm dice

2 carrots, peeled, cut into 1cm dice

80g baby spinach leaves

60g feta cheese, crumbled

Steamed couscous or rice, baby leaf salad, to serve