Coat a large nonstick skillet with cooking spray; add oil. Place over medium-high heat until hot. Add onion and garlic; saute 2 minutes. Add rice, and saute 2 minutes. Add water and saffron. Cover, reduce heat, and simmer 20 to 25 minutes or until liquid is absorbed and rice is tender. Stir in black beans and corn; cook 5 minutes or until thoroughly heated. Add salt and pepper.