In a large pot, bring salted water to a boil. Add the cubed potatoes and cook until tender, about 15-20 minutes. Drain and return to the pot.

Add butter, milk, and garlic powder to the potatoes. Mash until smooth and creamy. Season with salt and pepper to taste. Keep warm.

In a mixing bowl, combine the chopped spinach, artichoke hearts, cream cheese, Parmesan cheese, mozzarella cheese, minced garlic, lemon juice, salt, and pepper. Mix until well combined.

Preheat the oven to 375°F (190°C). Line a baking sheet with parchment paper.

Place the salmon fillets skin-side down on the prepared baking sheet. Use a sharp knife to create a pocket in each fillet.

Stuff each salmon fillet generously with the creamy spinach and artichoke mixture.

Bake the stuffed salmon in the preheated oven for 20-25 minutes, or until the salmon is cooked through and flakes easily with a fork.

Plate the buttery garlic mashed potatoes alongside the stuffed salmon. Garnish with fresh parsley.