Match the swap to your cooking method: choose a firmer fillet (grouper/halibut) for broiling or pan-searing, and a flakier mild fish (sea bass/cod) for gentle baking.
Use the same weight and similar thickness as your red snapper so doneness timing stays close.
If your substitute is leaner or softer (tilapia/pollock), lower the heat slightly or reduce cook time by 1–2 minutes per side to prevent dryness.
Boost flavor with lemon juice or a light herb-butter finish, especially for emergency swaps that can taste blander.
Check doneness by flake-test: the fish should separate into moist flakes and look opaque throughout.