In a large pot, melt margarine over medium heat. Add onion and cook until softened, about 5 minutes.

Add garlic and cook for 1 minute more.

Stir in diced tomatoes, vegetable broth, basil, garlic powder, onion powder, salt, and pepper.

Bring to a boil, then reduce heat and simmer for 20-25 minutes, stirring occasionally.

Use an immersion blender to blend the soup until smooth, or carefully transfer to a regular blender and blend until smooth.

Serve hot.