Cut bell peppers in half lengthwise; discard seeds and membranes. Place bell peppers and tomatoes, skin sides up, on a foil-lined baking sheet; flatten peppers with hand. Broil 15 minutes or until vegetables are blackened. Place peppers in a zip-top plastic bag; seal, and let stand 10 minutes. Peel peppers and tomatoes; chop. Place half of chopped peppers and half of chopped tomatoes in a blender; process until smooth. Set aside.
Heat oil in a saucepan over medium-low heat. Add onion and garlic; cover and cook 5 minutes. Add pureed vegetables, remaining chopped bell peppers and tomatoes, tomato juice, 1 tablespoon marjoram, salt, and pepper; cook over medium heat until thoroughly heated. Garnish with marjoram sprigs, if desired.