How to Make It
In a large nonstick skillet, heat the oil until shimmering. Add the onion, garlic, chile and a generous pinch of salt and cook over moderate heat until the onion is softened and just lightly browned, about 8 minutes. Add the tomatoes and oregano and cook until the tomatoes just start to break down, about 5 minutes.
Season the shrimp with salt. Nestle them in the tomato sauce and cook over moderate heat, turning once, until just curled and opaque throughout, about 4 minutes. Add the cheese and cook over low heat, stirring, until the cheese is melted. Season the queso fundido with salt, transfer to bowls and serve at once, with warm tortillas.