1.In a large saucepan, warm oil over medium heat. Add onion and sauté, stirring often, until translucent, about 4 minutes. Stir in garlic and sauté until fragrant, about 30 seconds. Add in tomatoes, carrots, and celery and cook until tomatoes start to soften and release their juices, about 5 minutes. Stir in water, cashews, salt, and coriander.
2.Bring mixture to a boil, cover and reduce heat to medium low. Simmer mixture until carrots are tender, about 20 minutes.
3.Transfer mixture to a blender and purée until smooth and creamy. Pour back into saucepan and keep warm, stirring occasionally, over low heat.
4.Bring a large pot of salted water to a boil. Cook pasta to desired doneness and drain. Toss with a little olive oil before dividing among serving bowls.
5.Top servings of pasta with some tomato-carrot sauce and garnish with a grating of Parmesan cheese. Serve immediately.