Combine the first 3 ingredients in a small bowl and mix well to make the Seasoning Mix.
In a heavy 10-inch nonstick skillet over high heat, heat the oil just until it begins to smoke, about 3 to 4 minutes. Add the onions, bell peppers, and the turnips. Cook, stirring every 3 to 4 minutes, for 13 minutes, then add the jalapeños, poblanos (or other variety), garlic, and 3 tablespoons of the Seasoning Mix. Cook, stirring and scraping the bottom of the skillet thoroughly once a minute, for 3 minutes. Add the stock, scrape and stir well, then remove from the heat. Spread evenly on a sheet pan and refrigerate until chilled.
Season the crawfish (or shrimp) evenly with the remaining Seasoning Mix.
Preheat a 10-inch nonstick skillet over medium heat for 4 minutes.
Fold a tortilla in half, then open it up and spread 1 tablespoon sour cream evenly on one half of the tortilla, leaving an empty ½-inch border around the edge. Next, evenly spread ½ cup of the vegetable mixture over the sour cream, then add an even layer of crawfish tails (or shrimp), and top evenly with about 1⅓ ounces of the grated cheese (about 1/12 of the total amount). Next sprinkle a generous tablespoon of the sliced green onions over the cheese, and top that layer with 2 tablespoons of cilantro. Re-fold the tortilla closed and brush one side with melted butter.
Place the filled tortilla, buttered side down, into the preheated skillet. Brush the top side with melted butter and weight it with a pot lid or small, heavy plate. Cook, turning once, until golden and crisp, about 2-3 minutes per side. Repeat with the remaining tortillas and fillings. To serve, cut each cooked filled tortilla into 3 wedges.