Bring a large pot of lightly salted water to a boil. Preheat the oven to 350 degrees F. Lightly butter an 8"x 8" casserole and set aside. Add tortellini to the boiling water and cook until just tender.
While the pasta cooks, melt the butter in a pot over medium heat. Stir in flour until well combined.
While whisking steadily, slowly pour in the milk. Cook, whisking constantly, until mixture comes to a simmer and lightly thickens. Remove from heat and stir in cheese, tuna, paprika, oregano,salt and pepper.
When cooked, drain the tortellini well and place in the casserole. Spoon over the sauce. Sprinkle with the breadcrumb/cheese mixture. Bake 20 to 25 minutes, until bubbling hot and golden brown.
Note: The milk can be warmed in the microwave. Preheating the milk makes the sauce come to a simmer more quickly and less likely to burn on the bottom.
Options: Instead of spinach, cheese-filled tortellini, use a different type in this recipe, such as rainbow tortellini. Try another type of tangy cheese in this dish, such as Asiago or provolone. Instead of tuna, use one cup of small salad shrimp, or one cup of cubed ham in this recipe.