Heat olive oil in a large pot over medium heat. Add the chopped onion and cook for about 5 minutes until soft.
Stir in the minced garlic and diced carrots. Cook for 1-2 minutes until the garlic is fragrant.
Add the broccoli, cauliflower, and diced potato to the pot. Sprinkle flour over the vegetables and stir for about 2 minutes to coat evenly.
Pour in vegetable broth and half-and-half. Bring the mixture to a boil, then lower the heat and let it simmer for 15-20 minutes until the vegetables are tender.
Stir in lemon juice and shredded cheddar cheese until the cheese melts. Season with salt and pepper.
Use an immersion blender to blend half of the soup, leaving some chunks intact. Adjust the seasonings. If the soup is too thick, add a splash more of broth or half-and-half as needed.
Serve warm, garnished with parsley and extra shredded cheese. If desired, sprinkle on the crumbled bacon.