Bring a large pot of water to boil and cook spaghetti according to instructions on package.
Add 1/2 cup water, onion, garlic and thyme to a pan. Cover and cook over medium-low heat about 5-7 minutes.
Meanwhile, place canned tomatoes into a bowl and gently crush with fork or hands. When garlic is fragrant, add tomatoes to the pan. Partially cover and simmer over medium heat. Skim off any foam produced by the cooking tomatoes.
When al dente, drain pasta while reserving 1/4-1/2 of the water used for cooking. Add water to the sauce and stir, then add drained spaghetti and basil to the sauce.
Taste and adjust seasonings as desired. Remove from heat and serve.