Bring 1 ¾ cups water to a boil in sauce pan with tight fitting lid. Add rice and pinch of salt. Cover and reduce heat to a summer. Cook for 12 minutes or until water is absorbed.
While rice is cooking, prepare crema. Combine sour cream and cilantro, add salt and pepper to taste.
Heat oil in a medium saute pan over med-high heat. Add onions and garlic and saute until soft. Add corn, cumin, ¼ cup chopped cilantro, then add cooked rice and stir to combine.
Stuff filling into the avocados, heaping over the top. Drizzle with crema. Serve with small flour tortillas.