1. Combine first 3 ingredients in a large saucepan. Bring to a boil; reduce heat, and simmer 10 minutes.
2. Heat oil in a large nonstick skillet over medium-high heat. Add onion and garlic; sauté 3 minutes or until tender. Add rice; sauté 3 minutes. Add broth mixture. Bring to a boil; reduce heat to medium, and simmer 15 minutes.
3. Add tomatoes, mussels, and shrimp; cook 5 more minutes or until mussels open, stirring occasionally to break up tomatoes. Stir in peas; cook 1 minute or until thoroughly heated. Discard any unopened shells. Let paella stand 5 minutes.