Adjust an oven rack to the middle position and preheat the oven to 350°F (175°C). Spray a 9×13-inch baking pan with nonstick spray.
Pour about 1 cup of the marinara sauce into the bottom of the prepared pan and spread into an even layer.
Arrange the 12 chicken tenders in a single layer on top of the sauce in the pan.
Pour the remaining marinara sauce evenly over the chicken.
Bake the chicken at 350°F for 30–45 minutes, until the internal temperature reaches 155°F (use an instant-read thermometer). Baking time varies with tender size.
While the chicken bakes, bring a large pot of salted water to a boil and cook the 16 oz spaghetti according to package directions; drain in a colander.
When the chicken reaches 155°F, remove the pan from the oven and switch the oven to Broil. Top each piece of chicken with a mound of shredded mozzarella and a sprinkle of grated Parmesan.
Return the pan to the oven and broil, watching closely, until the cheese melts and the chicken reaches 160–165°F.
Transfer the chicken to a rack and let rest for 5 minutes.
Serve the baked chicken and sauce over the cooked spaghetti and garnish with chopped fresh basil and extra grated Parmesan if desired.