Heat oil in a large quart pot over medium heat. Add the onion and cook until translucent, about 2-3 minutes. Add the rest of the vegetables and cook for 5 minutes, stirring occasionally.
Add tomato paste and Italian seasoning and stir until well-incorporated.
Add the tomatoes, water, and lentils, stir and bring to a boil. Reduce heat to low, cover, and cook for 25-30 minutes, stirring occasionally.
In the meanwhile, place a pot of water on the stove, bring to a boil, and cook pasta. Set aside.
Once sauce has cooled, transfer to a blender and blend until smooth. You can also keep it chunky depending on your preference.