Heat a Dutch oven or large saucepan over medium-high heat. Add oil; swirl to coat.
Add onion and garlic to pan; sautÃ© 3 minutes or until onion starts to brown.
Add tomatoes, stock, oregano and pasta, in that order. Bring to a boil. Add noodles; stir to submerge in liquid.
Cover, reduce heat to medium-low, and cook 7 minutes or until pasta is almost done.
Uncover; stir in salt. Add spinach in batches, stirring until spinach wilts. Remove from heat; let stand 5 minutes. Sprinkle with cheese and serve.
Swap out spaghetti for any short pasta shape, such as elbow macaroni, rotini, or shells.
Use fresh grape tomatoes instead, and add fresh herbs.
Try adding chopped skinless, boneless chicken thighs, ground beef, or ground turkey for a heartier dish.
More chicken stock may be needed to completely submerge the noodles. This could definitely use more spinach (or other veggies) and cheese.