Can I take your order: a Chipotle concept conund
Python 3, 293 bytes

j=input();a,b,c,d,e,f,g,h,i=[1-ord(c)%7%5for c in j];print('\n'.join(('burrito'+[' bowl',''][a]+' with:',['pinto','black'][b]+' beans',['brown','white'][c]+' rice',['sofritas','chicken','steak'][d],['medium','mild','hot'][e]+' salsa'))+'\ncorn'*f+'\nguacamole'*g+'\nsour cream'*h+'\ncheese'*i)

Mostly basic lookups with a little modulo trickery for the indexes of items:
AB123YN yielding indexes -1,-2,1,0,-1,1,0 respectively, and
using string multiplication for the optional items rather than a lookup.