If you’re ok with
premeditated
cooking, here’s a couple easy ones
1. Salmon - grab a skin-on nice fat filet and soak it in sweet chili sauce for about 2hrs prior to cooking, slap it on the grill skin down, and every couple minutes pour some of the marinade leftovers ontop, it’ll come out retaining very few of the totals cals in the sauce used but a nice sticky coating of flavor ontop, just slide a long spatula under the fish and the skin will stay on the grill. (buy decent quality as stated above)
2. Breaded cod - cod filet, pat dry, coat in your favorite seasoned breadcrumbs on all sides, bake until browning on the outside, drizzle lemon juice on top (super lean, heartier than tilapia and not a bottom feeder)
3. Tuna and swordfish are great for individual meals, no so much for meal prep IMO - tuna needs nothing but some salt and pepper, a sear on both sides, and some soy sauce. Swordfish is great in a balsamic vinegar sauce (I do it with grape tomatoes and spinach cooked in the balsamic). Both of these cook like steaks, not fish.