How to Make It
Preheat the oven to 400°. In a medium skillet, heat the olive oil. Add the sausage, and cook over moderately high heat, breaking up the meat with a spatula into small crumbs, until browned and cooked through, 5 to 7 minutes.
In a medium saucepan, combine the water, milk, vegetable oil and salt and bring to a simmer. Remove from the heat.
Place the sour tapioca flour in a large bowl and briskly mix in the hot milk mixture with a wooden spoon until the flour is completely incorporated and a sticky dough forms. When the dough is cool enough to handle, knead it until smooth and just slightly warm.
Add the eggs one at a time, kneading and then mixing with the wooden spoon until incorporated. Stir in the grated cheese in two additions.
Using an ice cream soup and greased hands, shape the dough into 1/4-cup size balls and arrange evenly on two parchment paper-lined baking sheets. Bake until puffed and golden, about 20 minutes. Let cool slightly on the baking sheets.
Cut the cheese breads in half. Fill with the roast beef, red peppers and arugula. Place toothpicks through the top of the cheese rolls to hold them together. Serve immediately.