Coat a large nonstick skillet with cooking spray; add margarine. Place over medium-high heat until margarine melts. Add chopped onion, and sauté until tender. Stir in jalapeño pepper, ginger, and garlic; sauté 2 minutes. Add curry powder; sauté 2 minutes. Add tomatoes; cook over medium heat 5 minutes or until slightly thickened, stirring often. Stir in yogurt, salt, and white pepper. Add shrimp; bring to a boil. Reduce heat, and simmer 5 minutes or until shrimp are done.
Spoon mixture over rice; sprinkle with onions. Serve immediately.
Tip: To save time, you can buy shrimp that has already been peeled and deveined. You'll need 2 1/4 pounds peeled shrimp to equal 3 pounds unpeeled.