Heat the olive oil in a large pot over medium heat. Add the onion and cook for 3 minutes until it softens.
Stir in the garlic and cook for 1 minute until fragrant.
Add the lentils and vegetable broth. Bring to a boil, then reduce to a simmer. Cover and cook for 20 minutes.
Stir in the white beans, asparagus, thyme, salt, and pepper. Simmer uncovered for 8 minutes until the asparagus is tender but still bright.
Remove from heat. Stir in the lemon zest and juice. Taste and adjust salt if needed.
Sprinkle with fresh parsley before serving.