Preheat oven to 400 F. Line the baking sheet with parchment paper. Trim ends of Brussel sprouts and remove yellow leaves. Then, slice all Brussel sprouts in half.

In a medium bowl, combine halved Brussel sprouts, 2 tablespoons of olive oil, salt and pepper to taste, and toss to combine. Spread Brussel sprouts on the baking sheet, cut sides down, without crowding.

Roast in the preheated oven at 400 F for about 20 minutes.

If chicken tenderloins are too thick, slice them into strips. Season the chicken with smoked paprika, salt, and freshly ground black pepper.

Heat 2 tablespoons of olive oil on medium heat in a large cast-iron skillet. Add the chicken in one layer and cook for about 3 minutes. Flip the chicken strips over and cook for 2 more minutes.

Lower the heat to low, sprinkle the chicken with Italian seasoning and crushed red chili pepper flakes, add minced garlic, freshly squeezed lemon juice, and 3 tablespoons of butter. Cook for another 2 minutes or more, frequently stirring, until the chicken is cooked through but not overcooked.

Add roasted Brussel sprouts to the same skillet with cooked chicken. Add 1 remaining tablespoon of butter and melt it on low heat, stirring it together with the Brussel sprouts. Do it rather quickly, for a couple of minutes, just until the butter melts and the lemon garlic butter sauce coats both the chicken and the Brussel sprouts evenly. Remove from heat.

Stir in half of the chopped fresh parsley. When serving, top with the remaining half of chopped fresh parsley. Season with more crushed red chili pepper flakes, if desired.