In a large pot over medium heat, combine onion, yellow pepper, garlic, zucchini, and beef broth. Bring to a boil.
Reduce heat to low, cover, and simmer for about 20 minutes, or until zucchini is tender.
Remove from heat. Use an immersion blender to purée the soup until smooth.
Stir in paprika, salt, and pepper.
Ladle into bowls and top with a spoonful of sour cream and a sprinkle of parmesan cheese. Serve warm.