In a heavy saucepan over medium heat, combine tomato juice with ground red pepper, salt, black pepper and sugar. Add agar flakes. Cook and stir mixture until agar is completely dissolved. Remove from heat and let cool 15 minutes.
Stir in chopped onions, celery, cucumber and minced chili peppers. Pour mixture into lightly greased 5-cup mold and refrigerate until chilled and set.
Serve on a bed of shredded romaine lettuce, with a generous dollop of Avocado Lime Mayonnaise.