Cook pasta according to package directions, omitting salt and fat.
Heat oil in a Dutch oven over medium heat. Add garlic; sauté for 4 minutes. Add the clam juice, red pepper, and tomatoes. Bring to a boil. Reduce heat; simmer, uncovered, 5 minutes.
Add mussels; cover and cook 3 minutes or until shells open. Discard any unopened shells. Stir in tomato paste, and cook for 2 minutes, uncovered, or until sauce thickens.
Drain pasta, and place into each of 4 bowls. Top with mussels and sauce. Serve with parsley.