12 oz boneless, skinless chicken breasts
8 brown rice or whole-grain lasagna noodles (NOTE: Oven-ready noodles will work here as well; see instructions.)
8-oz chopped spinach, divided
1 14½-oz can or jar unsalted diced tomatoes, drained
3/4 tsp ground black pepper, divided
3/4 tsp sea salt, divided
1/2 cup whole-milk ricotta cheese
2 tbsp organic unsalted butter
1/4 cup white whole-wheat flour
2 1/4 cups whole milk
1 tbsp fresh lemon juice
1/3 cup grated Parmesan cheese
Preheat oven to 400˚F. Bring a large pot of water to a boil; add chicken and reduce heat to medium to maintain a low simmer. Cook until chicken is no longer pink inside and an instant-read thermometer reads 165˚F when inserted in center, 10 to 15 minutes. Using tongs, transfer chicken to a cutting board to cool slightly. Using 2 forks, shred chicken into bite-size pieces.
Meanwhile, bring a separate large pot of water to a boil. Add lasagna noodles and cook until pliable, about 8 to 9 minutes or 3 to 4 minutes if using oven-ready noodles. Drain and rinse under cold water. Mist a baking sheet with cooking spray and spread noodles in a single layer on sheet.
Mist a 9- by 9-inch baking dish with cooking spray and set aside. In a large bowl, stir together half of spinach, tomatoes, ½ tsp pepper, ¼ tsp salt and shredded chicken. Spread 1 tbsp ricotta along the length of 1 noodle, followed by about 5½ tbsp chicken-spinach mixture; roll up noodle and place in prepared baking dish. Repeat with remaining filling and noodles.
In a large saucepan, melt butter on medium. Add flour and cook, stirring constantly, for 1 minute. Slowly whisk in half of milk and bring to a simmer. Cook, whisking, until liquid starts to thicken, 1 to 2 minutes. Slowly whisk in remaining half of milk and cook, whisking, until thick enough to coat the back of a spoon, 2 to 3 minutes. Stir in lemon juice, remaining half of spinach and remaining ¼ tsp pepper and ½ tsp salt.
Pour milk mixture over lasagna rolls and sprinkle with cheese. Cover with foil and bake for 15 minutes. Uncover and bake until sauce is bubbling and cheese is melted, about 5 minutes. Let stand for 5 minutes before serving.