In a large saucepan, heat the olive oil. Add the onion and cook over moderate heat, stirring frequently, until softened, about 6 minutes. Add the smoked paprika, cumin and coriander and cook for 1 minute, stirring. Add the drained lentils, tomatoes and 1 cup of water; season with salt and pepper and bring to a boil. Cover and cook over low heat until the lentils are nearly tender, about 20 minutes. Stir in the squash, cover and cook over low heat until the lentils and squash are tender, about 15 minutes. Stir in the spinach until wilted, then serve.