Preheat the oven to 400°F (200°C).
Line two large rimmed baking sheets with parchment paper.
In a medium pot, heat oil over medium heat. Add the red onions and 1 tsp of the salt; sauté for 3 minutes. Add the celery and sauté until the onions and celery are softened, about 3 minutes. Add the lentils and water and bring to a simmer, stirring. Reduce heat, cover and simmer, stirring occasionally, for 10 minutes.
Stir in the tomatoes, basil, capers, garlic, vinegar, lemon juice, chili flakes and remaining salt. Simmer, uncovered, stirring often, until the lentils are tender, about 15 minutes. Season with more salt or chili flakes to taste.
Meanwhile, in a large bowl, toss the zucchini noodles with the olive oil and salt and pepper to taste. Arrange the noodles on the prepared pashto that they are lying flat (overlapping is ok). Place both pans in the oven and roast until the noodles are steaming and softened, about 5 minutes.
Serve the noodles topped with the Lentil Bolognese, sprinkled with salt and chili flakes, if using. Garnish with additional olive oil and basil as desired.