On a large pan, adjust the stove to high heat and add the Italian sausage and garlic. Use a wooden spatula to break apart the sausage as it cooks. You do not need to add any oil since the sausage has a lot of fat in it already. Let this cook on high heat for about 30 seconds.
Add in the tofu and gently stir until the meat begins to brown.
Add water, shoyu, salt, and sugar. Cover and stir occasionally for 3 - 4 minutes.
Uncover and slowly add the thickening agent. Let it cook on high for another minute to allow the cornstarch to cook. Turn off the stove and add green onions and sesame seed oil.