Cook pasta according to package directions. Drain and set aside.
In a saucepan, heat oil over medium heat and add onions. Cook for 5-6 minutes, until tender and lightly golden brown. Then add sausage, breaking it up with your hands (remove casing if there is any) and cook for another 2-3 minutes, until aromatic and the sausage is golden brown.
Add fennel seeds and thyme to the pan and sauté for another 2 minutes. Lower heat to a simmer and add cream, stirring to combine. Add salt, pepper and lemon juice to taste.
Add cooked pasta to the pan along with a splash of pasta water (or as needed). Finish with vegan parmesan, to taste and lemon zest.