What's the adjectival form of "sauce" as "salty" is to "salt"?

I'm not sure what the objection to using saucy is all about. Merriam-Webster says:

saucy adj
1: served with or having the consistency of sauce
2a : impertinently bold and impudent
b : amusingly forward and flippant : irrepressible
3: smart, trim <a saucy little hat>

The very first definition is exactly the meaning you are looking for. Sure, the word has other meanings, but most words have multiple meanings. If your food is too saucy, then just say so.

How about "over-sauced"?

While the suggestion "swimming in sauce" as suggested by nico is the probably the most idiomatic option, it's colloquial and might not be the best choice if you were speaking, say, formally in a kitchen or in a restaurant review.

As mentioned above also, "saucy" is an old term meaning "pert" or "impudent." Yet, the primary definition offered by Merriam-Websters is "served with or having the consistency of sauce." So given these prior meanings, whatever solution devised will be a nonce coinage.