How to Make It
Cut off the top 6 inches of each romaine leaf; reserve the bottoms for another use. In a medium saucepan of boiling salted water, blanch the romaine tops for 2 seconds. Using tongs, transfer the leaves to paper towels to drain.
In a medium skillet, heat the corn oil. Add the poblanos, garlic and onion and cook over moderate heat, stirring occasionally, until very soft, about 10 minutes. Stir in the chopped oregano and season with salt and pepper.
Heat a grill pan. On a work surface, arrange the romaine leaves in pairs facing in the same direction and overlapping slightly. Place one-fourth of the queso oaxaca and the poblano mixture in the center of the leaves and sprinkle with the oregano leaves. Fold the leaves over to enclose the fillings and wrap the stuffed romaine bundles in foil.
Grill the tamales over moderately high heat until the cheese is melted, about 3 minutes per side. Unwrap the tamales and transfer to plates. Spoon refried beans alongside and dollop with the sour cream. Scatter chopped tomatoes and parsley over the beans and serve.
Queso oaxaca is a stretched curd cheese that's wound into balls and often used for melting in quesadillas. Queso blanco is a firm, mild cheese. Both are available at Latin markets.