I’ve been on a vegan diet for 20 years. If you’re flying United (hit 1K this year!), pack your own food ... especially on long haul. Otherwise, your best bet for good food on *A as a vegan is to fly BR or SQ on TPAC flights. They have acceptable food in both Y and J ... they have actual cooked vegetables and usually tofu.
Most of the time, when I know I’m traveling for a whole day, I pack a completely separate tote with all of my meals, never expecting to rely on airline/lounge food. Marinated/roasted tofu and seitan, seeds, nuts, salt/pepper, and avocados. Always making sure to finish any fresh fruits/veg before clearing customs/ag inspection.
Last two SFO-SIN flights and IAH-LIM on United have not loaded special meal request. Doesn’t really matter, I have my food, and I get compensation for meals I probably wouldn’t have eaten anyway. Flight back from LIM served me cold chickpeas and cold, undercooked eggplant for both servings in J