Combine the chicken broth and 1 cup water in a small saucepan and bring to a simmer. Reduce the heat; hold at a gentle simmer.
Melt the butter in a medium pot over medium heat. Add the onions and cook until soft and translucent, 3 to 5 minutes. Stir in the thyme, cumin and orzo, and toast the pasta for 2 to 3 minutes. Carefully pour in the simmering broth and stir to combine. Bring to a simmer, then cover the pot and reduce the heat to medium low. Cook until all the liquid is absorbed, 20 minutes. Fluff with a fork.
Fold in the cherries, pistachios, lemon zest, olive oil and mustard greens. Top with parsley to serve.