Lay a piece of foil out and place salmon on top, then cover with tomatoes and pepper slices. Sprinkle with lemon juice if using. Wrap in foil, seal and cook for between 20 and 30 mins until fish is cooked through.
Check that there are no bones in the salmon. Flake and mash the salmon and mix with the pepper and tomato.
Prepare the couscous – place in a bowl, pour over about 200ml of water, mix in the butter, cover and leave for five minutes. Use a fork to fluff up the couscous.
Mix the fish, vegetables and couscous (or rice) together and then mash the mixture before serving.
Make sure to mash well so there are no large lumps of fish or vegetable.