Heat the oil over medium-high heat in a sauce pan. Cook the beef. Remove the meat from the pan with a slotted spoon. Add the onions to the pan and saute until the onions are soft, about 5 minutes.
Add the garlic and red bell pepper and cook for 5 minutes more. Add the tomato paste, cilantro, parsley and tomato sauce. Stir and cook for 2 minutes more.
Season with salt and pepper. Return the meat to the pan and cook over medium-low heat for about 30 minutes until the beef is fully cooked.
Pre-heat the oven to 400 degrees F.
Place the yuca into pieces and place into a pot of cold, salted water. Bring the water to a boil and cook it until is tender, about 10 minutes. Drain the yuca and return it to the pot.
Add the butter, milk and mash it to make a puree. Season with salt and pepper.
Spread half of the mashed yuca evenly in a baking dish.When the meat is ready, put it on top of the yuca and spread the remaining mashed yuca evenly all over the top. Add the cheeses over the yuca and bake the casserole until the top is golden, about 20 to 25 minutes.