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.