Bring a large pot of salted water to a boil. Add the spaghetti and cook according to package instructions until al dente. Reserve 1 cup of pasta water, then drain the pasta in a colander.

In a large skillet, heat the olive oil over medium heat. Add the chopped onion and sauté for about 3 minutes until translucent. Stir in the minced garlic and cook for another minute.

Add the halved cherry tomatoes to the skillet and cook for 5 minutes until they start to soften. Then, add the fresh spinach and cook until wilted, about 2-3 minutes.

Add the drained spaghetti to the skillet with the vegetables. Toss everything together, adding reserved pasta water as needed to create a light sauce. Season with salt and pepper to taste.

Serve the pasta warm, topped with grated parmesan cheese.