Spray a 9x13 baking pan (preferably glass) with cooking spray. Spread tomatoes (undrained) in pan.
Spread onions and garlic over the tomatoes.
Sprinkle salt, pepper, basil, thyme and oregano over the top.
Drizzle olive oil over the top, getting a good coating on the herbs so they won't burn.
Roast in a 300° oven for 3 hours until the tomatoes are carmelized.
Pour into a saucepan and blend with a stick blender until smooth. (Or blend in a blender or food processor).
If sauce is not as thick as you like, simmer until reduced to your liking, then taste and adjust seasonings if necessary.