If starting with uncooked rice: In a small saucepan, place the rice in two cups water and bring to a boil. Reduce to a simmer and cook for 12 to 15 minutes, or until the water has been absorbed. Remove from heat and allow the rice to stand for another 10 minutes before transferring it to a bowl to cool.

If starting with uncooked lentils: Cook the lentils in a small saucepan in two and a half cups water. Bring the mixture to a boil, then lower the heat and simmer until the lentils are tender, about 15 to 20 minutes. Drain the excess water and allow the lentils to cool to room temperature.

To prepare the vegetables, heat the oil in a large sauté pan over medium-high heat. Add the onion, celery, carrot, and mushrooms and cook until they are tender, approximately 7-8 minutes. Once the vegetables are cooked, remove from heat and allow to cool to room temperature.

Preheat the oven to 350 degrees Fahrenheit. Grease a 9- x 5-inch loaf pan.

Place one heaping cup each of the cooked rice, lentils, and vegetables in the container of a food processor. Pulse 6 to 7 times until the mixture begins to form a ball and gets sticky. Transfer the mixture to a mixing bowl and add the remaining cooked lentils, rice, and vegetables. Stir in the egg, herbs, salt, and pepper. Scoop the mixture into the prepared pan and drizzle tomato or barbecue sauce over it.

Bake uncovered for 30 minutes, until the outside has a slight crunch. Remove from the pan and serve warm.