Heat olive oil in a skillet over medium-high heat. Add mushrooms and season with salt. Cook until golden brown and all liquid has been evaporated.
Add chopped onion and cook until onion is translucent. Add garlic, stir and cook until fragrant. Transfer mixture to a mixing bowl.
Mix in oats (cheese if desired), bread crumbs, parsley, "eggs," sea salt, black pepper, cayenne pepper, and oregano. Mix well until combined. If pressed, mixture should hold together.
Cover bowl and refrigerate overnight.
Preheat oven to 450 degrees. Line a baking sheet with parchment paper and set aside.
Measure out 2 tablespoons of mixture and roll into balls. Place on lined baking sheet.
Bake until meatballs are lightly golden brown, around 20-25 minutes depending on your oven.
Bring marinara sauce to a boil in a large saucepan; reduce heat to low. Gently stir meatballs into sauce until coated. Simmer meatballs in sauce until cooked through, 45 minutes to 1 hour. (this step is really important...don't skip!)
Meanwhile, cook pasta according to package.
Serve meatballs and sauce over cooked pasta.
Enjoy :)
Notes
This is a perfect way to introduce a plant-based meal to a meat-eating crew on meatless Monday :)