Season salmon completely with salt and pepper; in a large bowl mix together cream cheese, mozzarella, spinach, garlic powder, and red pepper flakes
Using a paring knife slice a slit in each salmon to create a pocket; stuff pocket with cream cheese mixture
In a skillet over medium heat, heat oil; add salmon skin side down; cook until seared, 6 minutes; flip salmon; add butter and squeeze lemon juice all over; cook until skin is crispy, 6 minutes; serve warm
