In a medium saucepan, combine the water and lentils. Bring to a boil then reduce to low heat. Cover and simmer for 30 minutes, until all or most of the liquid is absorbed and lentils are tender. Use a fine mesh strainer to drain off any remaining excess liquid. Transfer the lentils to a large bowl and set aside.

While the lentils cook, set a large skillet over medium-high heat and add the olive oil. When the oil is hot, add the mushrooms, celery, and onion. Cook for 5 minutes, stirring frequently until softened and the liquid from the mushrooms has evaporated. Add the garlic and cook for an additional minute. Set aside to cool.

Preheat the oven to 350°. Line a 9x5-inch metal loaf pan with parchment paper so that the edges of the paper hang over the sides of the pan.

Use a potato masher or a fork to mash the lentils; leaving a little chunkiness is good.

Add the mushroom/celery/onion mixture, quick oats, flour, basil, salt, black pepper, and onion powder. Stir to combine thoroughly; the mixture will be thick.

Press the loaf mixture into the prepared pan, smoothing the top to make it even. Bake for 45 minutes.

Meanwhile, prepare the glaze: In a small bowl, whisk together the glaze ingredients - ketchup, yellow mustard, and bbq sauce.

When the loaf has finished its 45 minutes of baking, carefully remove it from the oven and brush the glaze over the top of the loaf to cover it completely. Return the loaf to the oven and continue baking for an additional 10 minutes to set the glaze.

After removing it from the oven, allow the loaf to stand for 10 minutes in the hot pan. Then, using the excess parchment paper on each side, lift the lentil mushroom loaf out of the pan and set it on a flat surface. Cut into 1-inch individual slices and serve hot.