Smoked angelfish and potato frittata

Heat oil and butter and sauté onion until transparent, about 5 minutes.
Add potatoes and stock powder and cook until just tender. (You may need to add a little water to prevent sticking.) Add baby marrows and cook, covered, for 3 to 4 minutes.
Lightly fold in fish and add lemon juice and pepper to taste.
Beat eggs, cream and milk together. Increase heat slightly and pour egg mixture over contents of pan.
Turn heat down to low and cook until eggs begin to set. Agitate mixture gently to ensure even cooking and avoid burning.
When almost set, place under a preheated grill and grill until egg in centre is cooked.
Sprinkle parsley over, cut into wedges and serve hot or cold, with a green salad.