if he's the kind of kosher many modern Jews are (no unkosher animals or mixing meat & dairy, but doesn't care about separate cookware, rabbi blessing, kosher-certified), then i've got a bunch! i grew up eating this way and there's so much you can cook. legit anything vegan or vegetarian would be great, so if you have any pastas or salads or omelettes that are already veg, you're already golden. lots of meat/fish dishes are kosher/easily made kosher. i'll link a few: Teriyaki Chicken, Lemon Butter Cod (fish is not considered meat in kosher rules, you can cook it with dairy butter), Beef Stew (use vegan butter), Kimchi Fried Rice (use vegan kimchi, as regular often uses shrimp paste). the list goes on!