Preheat oven to 200°C (180°C fan). Cook lentils in boiling water for 20–25 minutes until soft. Drain well and let dry.
Fry onions in olive oil for 10 minutes until soft. Add garlic and cook 2 more minutes. Transfer half to a food processor and keep the rest for sauce.
Wilt spinach with hot water, then squeeze out excess moisture.
Add lentils, spinach, pesto, and lemon zest to the processor. Blend until combined but slightly textured.
Pulse in pine nuts, then transfer mixture to a bowl. Mix in egg and breadcrumbs. Season well.
Shape into 20 balls and place on a greased tray. Bake for 15–20 minutes until golden.
For the sauce, add tomatoes, purée, vinegar, sugar, water, and basil to the onion pan. Simmer 15–18 minutes.
Cook spaghetti according to package instructions.
Add the Italian Veggie Balls to the sauce and gently coat. Serve over spaghetti with fresh basil.