1
HEAT oven to 375° F with rack in center position. Coat 13" x 9" x 2" baking dish with cooking spray. Heat oil in large skillet over medium heat. Add mushrooms and cook, stirring, until golden, about 6 minutes.
2
ADD onions, celery, and bell pepper (if using) and cook, stirring, until softened, about 5 minutes. Gradually add spinach and cook, stirring, until wilted. Transfer to large bowl.
3
PREPARE egg noodles al dente according to package directions. Drain and add to vegetable mixture along with tuna.
4
MELT butter in medium saucepan over medium heat. Add flour and cook, stirring constantly, until one shade darker, about 3 minutes. In a slow stream, add milk, whisking until well combined. Bring to a boil, reduce heat, and simmer until thickened, 5 to 8 minutes.
5
WHISK in Parmesan and lemon juice. Add to tuna mixture and stir gently to combine well. Season with salt and pepper.
6
SPOON into prepared dish and sprinkle evenly with Cheddar and breadcrumbs. Bake until bubbling around edges and top is golden brown, 20 to 25 minutes. Cool slightly before serving.
NUTRITION (per serving) 434 cal, 27 g pro, 51 g carb, 4 g fiber, 9 g sugar, 15 g fat, 7 g sat fat, 502 mg sodium