Vegetarian Mushroom Meatballs

Heat oil in a large skillet over medium-low heat. Saute onion in the hot oil, about 7 minutes. Add mushrooms, increase heat to medium-high, and cook and stir until water evaporates and they brown nicely, 10 to 15 minutes. Stir in garlic and transfer mixture into a mixing bowl; let cool.

Stir oats, bread crumbs, 1/2 cup parsley, eggs, broth, oregano, thyme, salt, and pepper into the mixture to combine. Cover with plastic wrap. Refrigerate for flavors and texture to develop, at least 2 hours, to overnight.

Preheat the oven to 400 degrees F (200 degrees C). Grease a rimmed baking sheet lightly.

Form small balls from the mixture using a tablespoon as a measure. Place on the prepared baking sheet.

Bake in the preheated oven until browned, about 15 minutes.

Meanwhile, heat marinara sauce in a medium saucepan over medium-low heat. Remove meatballs from the oven and transfer to the sauce; cook over low heat for 15 minutes more. Garnish with Parmesan cheese and/or 1 teaspoon parsley.