It's not even difficult, you just need to plan your meals and have a basic inkling of what nutritional requirements are.
Some combination of a legume and a whole grain can fulfill all your macronutrients. Lentils and rice, black beans and corn, etc. Then choose a vegetable that's high in iron, like broccoli or spinach.
These are just examples, but there are so many variations you can do on top of it.
A major part of the problem is how many vegans/vegetarians get upset whenever someone mentions "nutritional requirements." It's like it's a trigger word.
I get not wanting to listen to right-wing misinformation like "it's impossible for vegans/vegetarians to meet all their nutritional requirements," because that's bullshit. It's absolutely possible, and not even difficult. It just requires some intelligent planning.
But they don't stop at that. They also get upset whenever someone says "Meeting all your nutritional requirements as a vegan/vegetarian requires intelligent planning." This is completely irrational, because it does require planning. And it's a disservice and misinformation to say that it doesn't.
It's especially important for vegans and vegetarians to plan their meals to meet all their requirements. But when they get all offended and self-righteous about the suggestion, it teaches new vegans/vegetarians bad habits.
No, you can't just eat cheese-its and oreos. Teach people how to plan a full, balanced vegan/vegetarian meal, or shut the fuck up about it and let others who are doing it have the floor.
Another problem is the perception that anyone who talks about protein is a chud. Vegetarians and vegans need to talk about protein, because they need to be deliberate about where they're getting it from. It's not the same as when gym bros talk about protein.
But any time I mention it, people roll their eyes. It must be the same old misandry that says "this guy talking about protein must be a gym bro chud" and ignores the possibility that "this guy talking about protein might actually be vegetarian or vegan." Like, I'm a scrawny dude geeking out about lentils and broccoli, which do you fucking think I am?