noun which may take the genitive case particle 'no'
full of ingredients; hearty; substantial
Describes food, especially soups, stews, or rice dishes, that contain a generous amount of solid ingredients rather than being mostly liquid or plain.
This miso soup is full of ingredients, with plenty of vegetables.
Today's bento is a mixed rice dish with lots of ingredients.
たっぷり means 'plentifully' or 'amply', but is a general adverb; 具だくさん is a no-adjective specifically for food with many ingredients.
Standard spelling using だくさん as kana for the 'plentiful' part.
Kanji spelling for だくさん; less common but still seen.
Compound of 具 (gu, 'ingredient') and だくさん (dakusan, 'a lot, plenty'). The だくさん part is a colloquial variant of たくさん (takusan).