Mayo, mustard, lettuce (as used here), salt and pepper are uncountable and that's why there's no article.
To be strictly logical, "tomatoes" should refer to whole tomatoes, while we should say "tomato" to mean slices of tomato. The same applies to "red onions". Still, it doesn't sound bad in the plural, I don't know why. Pickle (at least to my British ear) is a savoury jam-like substance and pickles would mean different types of this. In addition, pickles can be pieces of pickled vegetable.
Believer, may I correct your grammar? You use the present continuous at the beginning, but "manifest" is appropriate here. It's not an action going on, but a set situation. Further down, too, "are manifested", not "are being manifested".
Now a digression about spelling. There is a double "p" in the English word "pepper" but not in the Italian words
peperone (the big, sweet pepper) or
peperoncino (the small hot one). The plurals are
peperoni and
peperoncini. Before adding an "s" to a word which is already plural they could have consulted one of the millions of Italian-speakers who live in the USA! Unfortunately this is a well-established error. In Britain, and I imagine also in the USA, the word
pepperone doesn't even mean a vegetable but is applied to hot salame (that's another one:
salami is the plural again).
Cheers,
Lewis