Rinse the lentils thoroughly and place them in a medium-sized pot with the vegetable broth. Bring to a boil, then reduce the heat to a simmer. Cover and cook for about 25-30 minutes, or until the lentils are tender but not mushy. Drain any excess liquid.
While the lentils are cooking, heat a bit of olive oil (or use water for sautéing to keep it oil-free) in a skillet over medium heat. Add the chopped mushrooms, onions, and minced garlic. Sauté for 5-7 minutes, or until the vegetables are soft and the moisture from the mushrooms has evaporated. Remove from heat and let cool.
In a food processor, combine the cooked lentils, sautéed mushroom mixture, breadcrumbs, nutritional yeast (if using), tomato paste, Italian seasoning, dried basil, dried oregano, salt, and black pepper. Pulse until everything is well combined and forms a dough-like consistency.
Preheat your oven to 375°F (190°C) and line a baking sheet with parchment paper.
With your hands, form the mixture into golf ball-sized meatballs and place them on the prepared baking sheet.
If you prefer a slightly crispy exterior, lightly brush the meatballs with olive oil. Otherwise, you can omit this step for an oil-free version.
Bake the meatballs in the preheated oven for 20-25 minutes, or until they are firm and slightly browned on the outside.
Serve the vegan Italian meatballs with your favorite marinara sauce and pasta, or use them in sandwiches, wraps, or as an appetizer.