In a large saucepan bring 1 1/2 cups water to boiling; stir in rice. Reduce heat and simmer, covered, for 40 minutes or until kernels open. Meanwhile, coat corn with cooking spray. Grill on the rack of a grill or in a grill pan over medium-high heat for 7 to 8 minutes or until charred, turning frequently. Remove and cut corn from cob.
Drain rice, if necessary. Stir in corn, beans, walnuts, basil, oil, lime juice, salt and pepper. Stir to heat through. Remove from heat and top with avocado.