In Japan, tempura over rice is simply called tendon. It's a shortened word for tempura donburi. You can certainly use any veggies, herbs, fish, seafood for the topping. Normally, large shrimp along with several varieties of vegetables are made into tempura. I like using shiso leaves. Shiso is sometimes called perilla in English and is often used in sushi restaurants - looks like big leaves somewhat similar to large basil leaves but with more texture. I love the taste of shiso and although some people compare shiso leaves to mint, I don't find them similar. Some of the vegetables you can use for tempura include (but not limited to) Japanese eggplant, sweet green Japanese pepper called shishito, kabocha pumpkin, onion, carrots, zucchini, shiso leaves, mushrooms, shitake mushrooms, sweet potato, potato, green beans, and leafy veggie, etc. I am revising this recipe to change the batter ingredients to US measurement for easier preparation.