To a cast iron skillet over medium-high heat, add the oil and butter. Stir in the red chile flakes. Saute the onions and jalapeño until tender, 2-3 minutes. Add the garlic and stir until fragrant, but not browned, about 1 minute. Toss in the tomatoes and cook until the tomatoes begin to break down and release their juices, another 2-3 minutes. Add the chicken broth and bring to a simmer. Then, add the shrimp to the skillet and season with salt, cooking and tossing until shrimp just turn pink and are cooked through but still tender, being careful not to overcook. Add the lime zest, lime juice, and cilantro. Taste for seasoning and add more salt as needed. Serve promptly with crusty bread, or over rice or noodles.