Bring just to the boiling point, stirring constantly. Gradually whisk in the flour with a fork, and continue cooking and stirring until slightly thickened.
Stir in the peas, and let the mixture heat back up to a simmer while stirring constantly.
Mix in the salmon/tuna, and season with salt and pepper to taste.
Continue cooking and stirring until thick and heated through.
Serve over saltine crackers, toast or buttered egg noodles.