In a small bowl, stir together the 1 teaspoon Morton kosher salt, 1 ½ teaspoons garlic powder, 1 teaspoon paprika, 1 teaspoon onion powder, 1 teaspoon dried thyme, ½ teaspoon black pepper, ½ teaspoon brown sugar, and ¼ teaspoon cayenne pepper, if using.
Pat the chicken cutlets dry with paper towels. Sprinkle about ¼ to ⅓ teaspoon of the seasoning mixture total evenly over both sides of all four chicken cutlets. You want the chicken lightly and evenly coated, not heavily packed with seasoning. Save the remaining seasoning for another recipe. (See Note 2)
For easier cleanup, line a rimmed sheet pan with parchment paper. To preserve as much of the sauce as possible for spooning over the finished chicken, leave the pan unlined and lightly coat it with nonstick cooking spray instead. (See Note 3) Arrange the cutlets in a single layer on the prepared pan. Refrigerate uncovered for at least 30 minutes or up to 4 hours. If you do not have time to brine the chicken, continue with the recipe immediately.
Preheat the oven to 425 F (220 C).
Spread the ½ cup jarred Alfredo sauce evenly over the top of each cutlet. Divide the ¼ cup oil-packed sun-dried tomatoes and 1 cup baby spinach leaves among the cutlets, then sprinkle the ¼ cup freshly grated Parmesan cheeseevenly over the top.
Bake for 14–18 minutes, or until the thickest part of each cutlet reaches 165 F (74 C). Begin checking early if the cutlets are especially thin.
If desired, switch the oven to broil and broil for 1–2 minutes if you would like to brown the cheese. Watch the chicken closely to prevent burning.
Spoon any sauce from the sheet pan over the chicken. Finish with freshly cracked freshly cracked black pepper and a squeeze of lemon juice, if desired. Serve immediately.