Heat 1 tablespoon oil in a large saucepan over medium heat. Cook onion, stirring, for 3-4 minutes until softened. Add celery, capsicum, onion powder, paprika and oregano, then cook for 3 minutes or until fragrant. Add rice and toss for 1-2 minutes until coated in oil.
Stir in stock, tomato, Worcestershire and Tabasco sauces, then season. Bring to a simmer, then reduce heat to medium- low, cover and cook for 15 minutes or until rice is tender. Stir through ham and parsley for 2-3 minutes to warm through.
Heat remaining 2 teaspoons oil in a pan over high heat, season the prawns with cayenne and salt, then cook for 1 minute each side or until just cooked. Serve with rice and green leaves, if desired.