Learn Arabic (Modern Standard): هناك طعام لذيذ على الطاولة.

Because it is describing طعام, which is indefinite (it does not have ال). In Arabic, an adjective must match its noun in definiteness. Since we are saying general 'delicious food' and not 'the delicious food', both the noun and the adjective are written without ال.

How do we know to use لذيذ and not the feminine form لذيذة?

Adjectives must always match the gender of the noun they describe. The word for food, طعام, is masculine (notice it does not end in the common feminine marker ة). Therefore, we must use the masculine form of the adjective, لذيذ.

Why are the words ordered as طعام لذيذ instead of the other way around?

In Arabic, describing words (adjectives) always come right after the noun they describe. So instead of the English order 'delicious food', you build the phrase as 'food delicious'.

Where is the word for 'is' in هناك طعام?

Arabic does not usually use a word for 'is' or 'are' in the present tense. The word هناك means 'there', and when placed at the beginning of a phrase like this, it translates as 'there is' or 'there are'. Therefore, هناك طعام simply means 'there is food'.