Put the spaghetti in 1 liter of boiling water, add salt and oil. Cook for 10 minutes, rinse in cold water and drain into small pieces.
For the sauce, mix mayonnaise with ketchup, paprika, yoghurt and sugar, season with salt and pepper. Crumble the tuna into the sauce and mix in with its oil.
Quarter, core, wash and cut the peppers into strips. Eighth and core tomatoes. Mix the vegetables and pasta with the tuna sauce. Season the salad to taste and sprinkle with chives.