In a large skillet over medium heat, melt the butter (2 tbsp). Add the onion, bell pepper, green chiles, and jalapeño (if using) and sauté, stirring often, until softened, about 4 to 5 minutes. Stir in the garlic and sauté for another 30 seconds.

Stir in the salt, pepper, cumin, oregano, cayenne (if using), and heavy cream. Bring to a boil, lower the heat, and simmer for 10 minutes, stirring often.

Stir in the sour cream, 1 cup of the shredded cheese, and the lime juice. Remove from the heat and stir until the cheese is melted. Set aside.

In a separate saucepan or skillet, heat the butter over medium-high heat. Add the shrimp, scallions, salt, pepper, cumin, oregano, and cayenne (if using). Sauté, stirring often, until the shrimp are pink, curled, and cooked through, about 2 to 3 minutes. Don't overcook! Remove from the heat. Stir in ¼ cup of the prepared creamy sauce. Set aside.

Heat a thin layer of vegetable oil in a small skillet over medium heat. Using tongs or a spatula, quickly place a tortilla in the hot oil, then carefully flip, and then transfer to a plate lined with paper towels to drain. Flip on the paper towels, and then place them on a separate plate. The tortillas only need about 1 to 2 seconds per side in the hot oil. Continue with other tortillas, adding more oil as needed.

Preheat oven to 350°F (175°C).

Spoon a thin layer of the sauce over the bottom of your 9x13" baking dish.

Place a tortilla in the dish, and then place a layer of the shrimp filling down the middle of it. Roll it up, and place it seam-side down in the dish. Repeat until the dish is full.

Spoon the remaining sauce over the tops of the enchiladas, leaving a little of the tortillas uncovered at each end. Top with the remaining cheese.

Bake for 15 to 20 minutes, or until the cheese has melted and is bubbly.

Remove from the oven and let rest for 5 minutes. Top with chopped cilantro and extra chopped scallions. Serve hot with sliced avocados, jalapeños, and lime wedges, if desired.