The easiest spaghetti sauce

2 cans of whole stewed tomatoes
1/2 onion, diced and sautéed in olive oil
fresh basil

Easy one pot option:
Sautee onion in a deep non-stick wok, when the onions have reached a nice translucent, soft look add tomato liquid. When sauce is done add precooked pasta and heat till warmed. Add basil one minute before serving. Otherwise, fry onions and proceed to the next step.

After opening the cans of tomatoes drain the liquid into the sauce pan. To eliminate the slight bitter taste tomato seeds have, cut the tomatoes lengthwise and de-seed. Coarsely dice the flesh and place in the sauce pan. Let the liquid simmer in a pot till it condenses down add pepper and salt to taste.

When pasta is cooked and drained, add basil to sauce cooking for no longer than one minute. Serve sauce over pasta or mixed in.

If you want to avoid pasta, try baking spaghetti squash. Cut the squash in half and bake according to directions. Once it's done, scoop the stringy, noodle like insides onto a plate and serve with your homemade sauce. Its tasty and a great change from your normal spaghetti dish.
To accent this sauce and change or intensify the flavor add:
Oregano
Thyme
Red Pepper Flakes
Dried Italian Seasonings
soffritto made from carrots, onions, celery, garlic, olive oil, and seasonings
olives (canned black or fancy ones)

Protein options include:
Shrimp (low on fat and calories)
ground beef (aim for 98% lean or the sauce will be greasy)
vegetable protein (also low in fat and calories, and makes a nice vegetarian option)