Abuelita Rosa's, or jut Abuelita's Mexican Restaurant -they seem to call it both things. Most people just call it "Rosa's" 5603 South Pennsylvania, 1 1/2 miles N. of I-240 Oklahoma City. Strip mall. Be very careful to not confuse this delicious little place with "Abuelo's" in Bricktown. Abuelo's is very handsome and has great service and granite sculpture but the food is (except for the stuffed poblano wrapped in a tortilla and deep fried) not much.
Rosa's "special sauce" is a mix of fried jalapenos & onions, a little guac, and cilantro. You have to ask for it.
I recommend their steak taco (grilled steak tossed with a tiny bit of the special sauce and more cilantro) and the "handmade" pork tamales. The kind where you get chunks of corn kernels, not just cornmeal, and actual meat.