If baking today, preheat oven to 375 degrees Fahrenheit.
Preheat an oven-friendly pot (Dutch oven or similar) on medium-low heat. Add a little oil (if using) and the diced red onion with a big pinch of salt. Cook 10 minutes, stirring occasionally.
Add the minced garlic, thyme, and fresh ground pepper. Stir until fragrant, about 30 seconds.
Add the vinegar (or wine), stir 1 minute, scraping the bottom of the pot to detach caramelized bits.
Add the rice and stir well to coat. Turn off the heat. Pour in the hot vegetable broth and stir.
Cover the pot with oven-friendly lid (or wrap tightly with aluminum foil). Place in oven for 30 minutes. Or you can stop here, let the pot cool, refrigerate, and bake it later for about 40 minutes.
When done, remove the risotto from the oven – careful not to spill! Uncover and use a wooden spoon to stir energetically for 3 to 5 minutes. As you stir, the risotto will become more and more creamy. If too thick, add a little hot broth.
Stir in the nutritional yeast (starting with the smaller amount). Taste and adjust seasoning.
Stir in the baby spinach and green peas.
If not eating immediately, transfer to an airtight container and refrigerate.
At dinner time
Either sauté some mushrooms in a skillet on medium, perhaps with a half teaspoon of vegan Worcestershire sauce, roast some other vegetables, or reheat some leftover veggies (and/or other add-ins) that you cooked previously.
You can reheat the risotto itself in the microwave or in the skillet. In the latter case, you may need to add a little broth or a few tablespoons of unsweetened plant milk.