Place the pine nuts in a dry skillet over medium heat and toast for 2-3 minutes until golden and fragrant, then remove and set aside.
Season the chicken breast evenly with half of the sea salt and black pepper.
Heat half of the olive oil in the same skillet over medium-high heat and cook the chicken for 6-7 minutes per side until fully cooked through.
Transfer the chicken to a cutting board to rest for 3 minutes, then slice into strips.
Lower the heat to medium and add the remaining olive oil and minced garlic to the skillet, sautéing for 30 seconds until aromatic.
Add the baby spinach, remaining sea salt, and black pepper to the pan, tossing frequently until the spinach is just wilted.
Stir in the lemon juice and remove the pan from the heat.
Plate the sautéed spinach, top with the sliced chicken breast, and garnish with the toasted pine nuts and parmesan cheese.