To prepare a spinach beef cannelloni manicotti recipe, you'll first need to prepare the spinach. You can buy spinach at your local grocery store, or you can make it at home. Place 1 cup of spinach in the bottom of an 8 x 8-inch baking dish. Pour 2 tablespoons of olive oil into the pan. Add 1 tablespoon of minced garlic and 1 teaspoon of oregano. Cook and stir over medium-high heat until the garlic is fragrant, about 5 minutes. Remove from heat and add 2 cups of shredded Parmesan cheese. Season with salt and pepper to taste. Bake in 375 degree F oven for 20 to 25 minutes or until browned. Serve warm.