This is a nod to the nostalgia of our childhood TV dinner. But the difference here is fresh fish and our special tartar sauce, easily created from ingredients you likely have in the fridge.
Prepare a charcoal or gas grill for medium heat (350° to 450°; you can hold your hand 5 in. above cooking grate only 5 to 7 seconds). Set a cooling rack over half of cooking grate. In a small bowl, mix potatoes and 1 tbsp. oil. Spread potatoes on rack and grill until browned, turning occasionally, about 10 minutes.
While potatoes cook, make sauce and cook fish. For sauce, in a small bowl, mix capers, lemon juice, zest, and mayonnaise. Set aside.
Rub fish on both sides with remaining 1 tbsp. oil and sprinkle with 1/2 tsp. salt. Using a wad of oiled paper towels and tongs, oil clear portion of cooking grate. Lay fish on grate and cook, turning once, until grill marks appear and fish is opaque, about 5 minutes total.
Transfer potatoes and fish to a platter. Sprinkle potatoes with remaining 1/2 tsp. salt and the parsley. Serve with caper mayonnaise and lemon wedges for fish.
Note: Nutritional analysis is per serving.