Cut bell peppers in half lengthwise; discard seeds and membranes. Place pepper halves, skin sides up, on a baking sheet; flatten with hand.
Prepare grill. Place pepper halves and squash halves on grill rack coated with cooking spray; grill 5 minutes. Turn squash halves (do not turn pepper halves), and grill 5 minutes; remove peppers and squash from grill. (Peppers will be blackened.) Place peppers in a zip-top plastic bag; seal bag. Let stand 15 minutes. Peel peppers, and cut into 1-inch pieces. Cut squash into 1-inch pieces.
Bring broth and saffron to a simmer in a large saucepan. (Do not boil.) Keep warm over low heat.
Heat oil in a large Dutch oven over medium- high heat. Add onion golden, stirring frequently. Add garlic and rice; cook 2 minutes, stirring frequently. Reduce heat to medium. on; cook 3 minutes or until onion is
Stir in 2 cups broth mixture; cook 10 minutes or until liquid is nearly absorbed, stirring constantly. Add remaining broth mixture, 1/2 cup at a time, stirring constantly; cook until each portion of broth mixture is absorbed before adding the next (about 30 minutes total). Remove from heat. Add peppers, squash, tomato, and remaining ingredients during last 5 minutes of cooking time. Remove from heat; cover and let stand 5 minutes.