Instructions
1. Preheat the Oven:

Preheat your oven to 375°F (190°C). Grease a 9×13-inch baking dish with olive oil or non-stick spray and set aside.
2. Prepare the Haggis Filling:

In a medium bowl, combine the cooked and crumbled haggis with ricotta cheese (if using), Parmesan cheese, thyme, garlic powder, olive oil, and a pinch of salt and pepper. Mix well until everything is thoroughly combined. The haggis filling should be thick but spreadable.
3. Stuff the Cannelloni:

Carefully stuff the uncooked cannelloni pasta tubes with the haggis mixture. You can use a small spoon or a piping bag to fill them, being gentle to avoid breaking the tubes. If you’re using lasagna sheets, cut them into rectangles, roll them up with the filling inside, and proceed similarly.
4. Prepare the Arrabbiata Sauce:

In a large saucepan, heat 2 tablespoons of olive oil over medium heat. Add the minced garlic and red pepper flakes, sautéing for 1-2 minutes until fragrant (be careful not to burn the garlic).
Add the crushed tomatoes, oregano, sugar, and a pinch of salt and pepper. Stir to combine and bring the sauce to a simmer. Let it cook for 10-15 minutes, allowing the flavors to meld together and the sauce to thicken slightly.