PREHEAT oven to 400F. Cut foil twice the size of a large baking sheet. Lay half on sheet. (The other half will hang off the side.)
STIR olives with tomatoes, garlic, shallot, capers, oil, lemon zest and juice, dill and salt in a bowl. Arrange fish in a single layer on foil. Top fish with olive mixture. Cover with overhanging foil. Make overlapping pleats around edges to seal.
BAKE in centre of oven until a knife tip inserted into the thickest part of fish comes out warm, 13 to 15 min. Reserve 2 fillets and sauce for puttanesca fish stew. Serve remaining fish and sauce over quinoa.