1. Cut off tops of capsicums and remove seeds. In large saucepan, cook capsicums in boiling water for 2 minutes. Drain well. Stand capsicums, cut side up, in foil lined 33 x 23 cm (13 x 9-inch) baking pan. Set aside.
2. In large saucepan over medium heat, melt margarine. Add celery and mushrooms. Cook, stirring, for 3 minutes. Stir in cereal, rice, salsa and ricotta cheese.
3. Fill capsicums with rice mixture. Top each with 15 ml (1 tbsp) Cheddar cheese. Bake at 180°C (350°F) for about 30 minutes or until thoroughly heated. Serve hot.