Bring a large pan of salted water to the boil.
Meanwhile, heat the olive oil in a large frying pan over medium heat.
Add the chopped onion and sauté for 5-7 minutes, until translucent.
Add the sliced garlic and cook for 1 minute, taking care not to let it brown.
Pour in the tinned chopped tomatoes, season with salt and pepper, and simmer gently for 10-15 minutes.
When the water is boiling, add the tortellini and cook for 2-3 minutes, or until al dente, according to the packet instructions.
Stir in the single cream and allow the sauce to simmer for 2 minutes.
Add the spinach and cook for 1-2 minutes, until wilted.
Drain the tortellini and stir into the sauce, tossing gently to coat.
Serve immediately, scattering grated Parmesan on top to taste.