Chop the onion. Wash and trim sprouts, cut larger ones in half (or quarters, if very large.)
Heat oil in pan. Saute onion in pan until soft. Add sprouts to hot pan, and let brown, stirring occasionally. Add chestnuts, stir. Add 1/4 c water and let it simmer to finish cooking the sprouts.
Stir in cooked rice, add a pinch of salt, and heat through.