Zucchini noodles (zoodles) are readily available in many markets, or you can make them yourselves with either a mandolin or a spiralizer. (See 6 below.) Place in a bowl and set aside. Prepare marinara sauce.
Place onions in a large non-stick skillet over medium-high heat. Cover the skillet. Watch the onions as they cook, stirring often. At first, the onions will exude liquid and they will not stick to the pan. After a few minutes, as the liquid cooks off, the onions may start to stick. Just add water, one tablespoon at a time. Stir and re-cover. Cook just until the onions soften and start to brown around the edges, about 4 minutes.
This recipe was made to be oil-free. If you think Italian is not Italian without olive oil, either sauté your onions, garlic, and mushrooms in 1-2 tablespoons olive oil or add the oil to the dish after your tomatoes have cooked down. It is perfectly delicious with or without the oil.
Add garlic and mushrooms. Turn heat down to medium and cover. Cook until mushrooms soften, about 3 minutes. Stir often.
While onions and mushrooms cook, chop tomatoes into bite-sized chunks. Add to skillet when mushrooms are soft. (See note below about tomato selection.)
Simmer until the tomatoes have cooked down and begin to make a sauce.
Add seasonings except for fresh basil.
Make your zoodles by your chosen method. Follow the instructions of your mandolin or spiralizer. If using a potato peeler, start at one end of the washed, unpeeled zucchini. In one continuous movement, pare thin slices of the zucchini into a bowl.
Once your sauce has cooked down and is ready to be served, it’s time to cook the zoodles. Be careful not to overcook. It should only take about 3 minutes for the zucchini to heat and soften. If you have a steamer basket, use it to cook the zoodles fast but not too soft.
At this point, either serve the sauce over the zoodles or add the zoodles to the sauce and serve.
Note: You can use any tomato, but Roma tomatoes make the thickest, sweetest sauce. Peeling the tomatoes is optional. If you don’t like the peel, score the tomatoes with an X and place them in boiling water for no more than a minute. Immediately plunge them in ice water and take them out. The peels should slip right off.