What's the common denominator?

Our Advanced students are learning to turn out great-tasting dishes with any ingredients that Chef Dan can throw at them. Can you guess the secret ingredient that was at the heart of their challenge today?

Ruthann's stuffed pepper with golden & candy cane beet chips,
raita and bhaji.  

Caitlynn's timbal with onion bhaji, beet chips, and brocolli
stir fry with yellow peppers.

Sarah waits with her two identical plates
while Chef is critiquing her classmates' food.