Char the skins of the poblano chilies over an open flame. Place in plastic bag to steam (10 minutes). Under running water, peel skins off of chilies. Open peppers, seed and de-vein them. Cut into ¼ strips. Saute onion, chile strips, and garlic in oil until soft. Add cilantro, Crema Mexicana and cheese. Heat slowly over low flame. Serve with corn or flour tortillas.