Heat a large pot of water over high heat and bring to a boil. Season generously with kosher salt.
While the water heats, use a sharp knife to butterfly the sausages.
Add the pasta to the salted water and cook until al dente. Drain the pasta reserving some of the pasta water for later.
Heat a large skillet or flat top over medium high heat and coat with olive oil. Add the sausages, cut side down and cook until browned, breaking up with a spatula as needed. Remove them from the heat and set aside.
Add the cooked spaghetti to the skillet or flattop, along with a splash of pasta water and a few spoonfuls of sauce. Remove the pasta from the pan and build the burritos.
Build the burritos by dividing the spaghetti between the tortillas, topping the spaghetti with the sausage, more marinara sauce, and the mozzarella. Roll up the burritos.
Make the cheese skirt by sprinkling the remaining mozzarella into 4 rectangles on the flat top – if you’re working with a skillet, do this one at a time. When the cheese starts to brown around the edges, Add the burritos and roll the skirt around the burrito. Remove from the skillet and cool for 5 minutes to crisp the cheese.