Rinse the rice in a mesh strainer to get rid of the extra starch until water runs clear.
Add the rice and water into a small pot and place it on the stove, covered.
Bring the rice to a boil and lower to a simmer.
Cook for 15-20 minutes or until the water is completely absorbed. Prop the lid open but keep it on top and let the steam out. Set aside.
For the Tonkatsu Sauce
Combine the ketchup, Worcestershire sauce, soy sauce, garlic, and onion powder in a small bowl. Set it aside.
For the Zucchini Katsu
Add the egg, flour, and panko bread crumbs to separate bowls.
Salt and pepper the zucchini, then coat it in flour and shake off the excess. Next, dip it into the beaten egg and then firmly press it into the panko bread crumbs for a thick, generous layer of breading.
In a deep pan, add enough oil to deep fry the zucchini. Heat the oil to 340°F over medium heat to ensure the zucchini fully cooks without burning the bread crumbs.
Gently place it into the oil and deep-fry for 5 to 6 minutes per side or until the zucchini is fully cooked and the panko coating is golden brown and crispy.
Use a skimmer to clean up loose breadcrumbs and try to keep the oil temperature at 340°F. Repeat with the remaining zucchini and work in batches to avoid lowering the oil temperature.