Adjust rack to top position and preheat oven to 425 degrees. Wash and dry all produce. Dice potatoes into 1/2-inch pieces. Trim green beans. Mince or grate garlic. Quarter lemon. Mince chives. Heat a large, dry pan over medium-high heat. Add almonds and cook, stirring often, until golden brown and toasted, 3-5 minutes. Turn off heat; transfer to a small bowl. Wipe out pan.

Place potatoes in a medium pot with enough salted water to cover by 2 inches. Bring to a boil and cook until tender, 15-20 minutes. Reserve 1 cup potato cooking liquid, then drain well. Return potatoes to pot and mash until smooth. Stir in 1 TBSP butter (2 TBSP for 4 servings), half the crème fraîche, and half the chives; season with salt and pepper. Keep covered off heat until ready to serve.

While potatoes cook, toss green beans on a baking sheet with a large drizzle of olive oil; season with salt and pepper. Roast on top rack until softened and lightly browned, 12-15 minutes.

Meanwhile, pat salmon dry with paper towels; season with salt, pepper, and half the Italian Seasoning. Heat a large drizzle of olive oil in pan used for almonds over medium-high heat. Add salmon skin sides down and cook until browned and slightly crisp, 3-4 minutes. Flip and cook until salmon is opaque and cooked through, 3-4 minutes more. Turn off heat. Transfer salmon to a plate; tent with foil to keep warm. Wash out pan.

Melt 2 TBSP butter (4 TBSP for 4 servings) in same pan over medium heat. Add garlic and a pinch of remaining Italian Seasoning; cook until garlic is fragrant, 1-2 minutes. Add stock concentrate and 1/4 cup water (1/3 cup for 4). Bring to a simmer and cook until slightly reduced, 2-3 minutes. Squeeze in lemon juice to taste. Remove pan from heat and stir in remaining crème fraîche and chives. Season with salt, pepper, and more lemon juice to taste.

Stir a splash of reserved potato cooking liquid into potatoes to rewarm, if necessary. Toss green beans with almonds; divide between plates along with potatoes and salmon. Spoon sauce over salmon. Serve with any remaining lemon wedges on the side.