In a large skillet, heat olive oil over medium high heat. Add onion and garlic and cook until onion is translucent, about 5 to 7 minutes.
Add mustard seeds. Cook until mustard seeds begin to pop, about 1 to 2 minutes.
Stir in orzo, tomatoes, stock and chickpeas. Bring to a boil, then turn heat down and simmer, stirring frequently, until sauce has thickened and orzo is tender, about 20 minutes.
Stir in dill, salt and black pepper. Sprinkle with feta cheese. Serve.