Sorry you have to deal with that. It would be really simple for them to just set aside some extra toppings for you to add. Like they could easily make the big salad that they like and keep some toppings to the side for you to build your own. Maybe you could offer to wash the extra bowls needed for that. Idk why they wouldn’t be willing to do that or let you make your own dinner, sounds like they have a control problem
what youre feeling is perfectly valid! and you're right they could easily do more for you for ex when my mom made lasagna growing up there were ingredient my sibling likes that I don't so she would only put them on half of it, or when making a salad she'd put the ingredients that I don't like on after she had served me my portion you deserve better and I'm sorry you're having to go through this
im sorry you’re going through this. my parents did similar when i was younger and wanted to be vegetarian. my parents started making everything with meat and when it got to the point where i was losing weight bc they wouldnt buy anything without meat they forced me to eat chicken. and honestly that fucked up my relationship w food and them so i understand it fucking sucks. Theres not much I can say but be strong one day you will get out of there.
My mom has done similar for me too with chicken parm. For some reason I dislike the chicken tomato sauce cheese combo, so my mom will make one chicken without the tomato sauce. Sometimes she puts cheese on sometimes she doesn’t. It seems to me that OPs parent’s are a lil selfish or just want to exert their power over OP.