Preheat the oven to 375°F. In a large saucepan,combine the rinsed lentils and vegetable broth. Bring the mixture to a simmer over medium-high heat and reduce the heat to medium-low. Cover the saucepan and simmer for 20 to 25 minutes or until the lentils are tender. Drain any excess liquid and allow the lentils to cool slightly.

In a small skillet, heat the olive oil over medium heat. Add the finely chopped onion, celery and minced garlic. Cook the vegetables, stirring occasionally until tender. This takes four to five minutes. Remove the skillet from the heat and let the mixture cool slightly.

Place the cooked lentils and sautéed vegetables in the bowl of a food processor. Pulse the mixture until a smooth paste forms, scraping down the sides as needed to ensure an even texture. Transfer the lentil mixture to a large mixing bowl.

Add the quick-cooking oats, beaten egg, tomato paste, salt, dried oregano, dried basil and pepper to the lentil mixture in the bowl. Mix everything together thoroughly until all the ingredients are well combined. Shape the mixture into balls about 1-½ inches in diameter.

Fit a 15x10x1-inch baking sheet with a wire rack and coat it with cooking spray. Arrange the meatballs on the prepared rack, spacing them about 1 inch apart. Bake the meatballs for 15 to 20 minutes or until they are lightly browned and firm to the touch.

Transfer the baked meatballs to a large skillet. Pour in the marinara sauce and bring the mixture to a simmer over medium-low heat. Cook the meatballs in the sauce for six to eight minutes, or until the marinara is bubbly and heated through. Sprinkle with grated Parmesan cheese and fresh parsley before serving.