Preheat oven to 400 degrees. Lightly oil two 8-inch square (or other shallow 2-quart) baking dishes. In a large pot of boiling salted water, cook noodles until 2 minutes short of al dente; drain, and return to pot.
Meanwhile, in a 5-quart Dutch oven or heavy pot, heat oil over medium. Add bell peppers; season with salt and pepper. Cook until crisp-tender, 4 to 6 minutes. Add flour and cook, stirring, 1 minute. Gradually add milk, stirring until smooth. Cook, stirring occasionally, until mixture comes to a simmer.
Remove from heat; add mixture to noodles in pot, along with tuna, artichoke hearts, and scallions. Season with salt and pepper, and toss. Divide between prepared baking dishes, and sprinkle with Parmesan. Bake until golden and bubbling, about 20 minutes.
To Freeze: Prepare through step 3; cool to room temperature. Cover tightly with aluminum foil, and freeze up to three months.
To Bake from Frozen: Preheat oven to 400 degrees. Bake, covered with foil, until center is warm, about 2 hours. Uncover, and bake until top is browned, about 20 minutes more.
To Bake from Thawed: Thaw overnight in refrigerator. Preheat oven to 400 degrees and bake, covered with foil, until center is warm, about 30 minutes. Uncover, and bake until top is browned, about 20 minutes more.