Queso Fundido with Shrimp Tomatoes

Name: Queso Fundido with Shrimp & Tomatoes
Ingredients: 2 teaspoons extra-virgin olive oil; 1 small onion, halved and thinly sliced; 1 garlic clove, minced; 1 serrano chile—halved, seeded and thinly sliced; Kosher salt; 3 plum tomatoes, diced; 1 1/2 tablespoons finely chopped oregano; 2 dozen medium shrimp, shelled and deveined; 1 pound Monterey Jack cheese, shredded; Warm corn or flour tortillas, for serving