Preheat oven to 350ºF. Coat a 3-quart casserole dish with cooking spray.
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# Bring a large pot of water to a boil; add pasta, stir and bring to a boil again. Cook until pasta is completely tender, about 8 to 10 minutes; drain, return pasta to pot and set aside.
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Coat a large nonstick skillet with cooking spray; add onion and peppers. Sauté over medium-high heat, stirring frequently, until onions start to brown, about 5 minutes; add to pasta pot.
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Bring milk to a simmer in a small saucepan. Meanwhile, beat eggs in a small, heatproof bowl. Slowly pour half of warmed milk into eggs (while beating constantly); pour mixture back into saucepan. Cook over medium heat, stirring constantly, until mixture thickens to consistency of custard sauce, about 5 minutes; remove from heat. Stir in chives, paprika, salt and pepper; then stir seasoned sauce into pasta pot.
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Add salmon to pasta pot and spoon mixture into prepared casserole dish. Bake until mixture is piping hot and top is browned, about 20 minutes. Garnish with red pepper rings before serving if desired. Yields about 1 1/3 cups per serving.