Cook the pasta in a large pot of rapidly boiling salted water according to the packet instructions. Add the frozen vegetables when the pasta has 3 minutes left to cook.
Drain the pasta and vegetables, reserving some of the pasta water.
Prepare the gravy according to the packet instructions, using pasta water instead of plain water.
Stir in Marmite and stock into the gravy.
Combine the gravy sauce with the pasta and vegetables and add extra pasta water if needed for a silky texture.
Top with fresh herbs, leftover meat and grated cheese and devour!