Portobello mushrooms stuffed with rice, fried onion, sweetcorn, (add bacon for any meat eaters), and topped with cheddar cheese. You can also stuff peppers or tomatoes with the same mixture so there's a variety for everyone.
BBC good food five vegetable tagine is great. She can pick the pepper out (or she might not even notice it!). I'd have it with cous cous, but it would be fine with flatbreads or rice. You can have grilled halloumi/tofu/turkey with it if you want more protein. Easy to cater for both meat eaters and vegetarians.
I also do a nice veggie sausage casserole in the slow cooker, with carrot, celery, little potatoes (the tinned ones, sounds weird but works brilliantly), tin of tomatoes and vegetable stock and some sage, thyme and oregano. Serve with broccoli. Admittedly, it's TVP in the sausages, but I always cut the sausage into rings and one sausage per portion is actually plenty. Maybe not for hungry teens actually, but it's fine for me!
Omelettes, French or Spanish.