По-русски это значило бы "У Вас (или у тебя) есть определенные овощи?" Так можно, в принципе, сказать. Но так русские обычно не говорят, и Вас примут за иностранца. Потому что в таком случае должны будут обязательно задать встречный вопрос "Какие именно?" И Вы должны будете тогда уточнить, например сказать: "Картошка и лук". Поэтому проще сразу спросить "У Вас есть картошка и лук?"
In Russian it would mean "Do you (or you) have certain vegetables?" So you can, in principle, say. But so Russians do not usually speak, and you will be mistaken for a foreigner. Because in that case they will have to ask the counter question "Which ones?" And you will then have to clarify, for example, say: "Potatoes and onions." Therefore, it's easier to ask "Do you have potatoes and onions?"
It depends on what you mean by "Do you have the vegetables?" If you want a clarification on where the vegetables are (whether the person has them or not") the structure you'd use would be "Овощи у вас?"
If you mean that the person might have a bicycle, a flock of birds or some vegetables and you are asking if they have the vegetables, "У вас овощи?" might just work.
Let's just say this course works in a certain model where we try not to stretch the common sense too much. Sentences about having a pen, a box or an orange will mostly be about typical objects. There are circumstances where the languages do not work exactly the same.
- this form of expressing possession is essentially a "there-is" sentence. So having or not having есть, as well as the exact placement of "у вас" make a lot of difference. You can think of this use of "у" as converting the person into an imaginary "place" where some things may or may not be found, and where events may unfold.